Oracle Database Heterogeneous Connectivity User Guide

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Oracle&reg; Database
Heterogeneous Connectivity User’s Guide
11g Release 2 (11.2)
E11050-01
July 2009
Oracle Database Heterogeneous Connectivity User's Guide, 11g Release 2 (11.2)
E11050-01
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Contents
Preface ................................................................................................................................................................. ix
Audience.......................................................................................................................................................
Documentation Accessibility .....................................................................................................................
Related Documents .....................................................................................................................................
Conventions .................................................................................................................................................
ix
ix
x
x
What's New in Heterogeneous Connectivity User's Guide? .............................................. xi
Oracle Database 11g Release 2 (11.2) New Features............................................................................... xi
Oracle Database 11g Release 1 (11.1) New Features.............................................................................. xii
1
Introduction
1.1
1.2
1.3
1.3.1
1.3.2
1.3.3
1.3.4
1.3.5
2
The Information Integration Challenge ...................................................................................
How Oracle Addresses Synchronous Information Integration ..........................................
Benefits of Oracle's Solution for Synchronous Information Integration.............................
Remote Data Can Be Accessed Transparently.................................................................
No Unnecessary Data Duplication....................................................................................
SQL Statements Can Query Several Different Databases ..............................................
Oracle's Application Development and End User Tools Can Be Used .......................
Users Can Communicate With a Remote Database in its Own Language..................
1-1
1-2
1-3
1-3
1-3
1-4
1-4
1-4
The Role of the Heterogeneous Services Component
2.1
2.2
2.3
2.3.1
2.3.2
2.4
2.4.1
2.4.2
2.5
2.5.1
2.5.2
2.5.3
2.6
2.6.1
Heterogeneous Connectivity Process Architecture ...............................................................
Heterogeneous Services Agents................................................................................................
Types of Heterogeneous Services Agents ...............................................................................
Oracle Database Gateways .................................................................................................
Oracle Database Gateway for ODBC Agent ....................................................................
Heterogeneous Services Components .....................................................................................
Transaction Service..............................................................................................................
SQL Service...........................................................................................................................
Heterogeneous Services Configuration Information.............................................................
Data Dictionary Translation Views...................................................................................
Heterogeneous Services Initialization Parameters .........................................................
Capabilities ...........................................................................................................................
The Heterogeneous Services Data Dictionary ........................................................................
Classes and Instances ..........................................................................................................
2-1
2-2
2-2
2-2
2-3
2-3
2-3
2-3
2-4
2-4
2-4
2-4
2-5
2-5
iii
2.6.2
2.7
3
Features of Oracle Database Gateways
3.1
3.2
3.3
3.3.1
3.3.2
3.3.3
3.3.3.1
3.3.3.2
3.4
3.4.1
3.4.2
3.4.2.1
3.4.2.2
3.5
3.6
3.7
3.8
3.9
3.10
3.10.1
3.10.2
3.11
3.11.1
3.11.2
3.11.3
4
SQL and PL/SQL Support......................................................................................................... 3-1
Heterogeneous Replication ....................................................................................................... 3-2
Passthrough SQL......................................................................................................................... 3-4
Using the DBMS_HS_PASSTHROUGH Package ........................................................... 3-4
Considering the Implications of Using Passthrough SQL ............................................. 3-4
Executing Passthrough SQL Statements .......................................................................... 3-5
Executing Nonqueries.................................................................................................. 3-5
Executing Queries......................................................................................................... 3-7
Result Set Support....................................................................................................................... 3-9
Result Set Support for Non-Oracle Systems .................................................................... 3-9
Heterogeneous Services Support for Result Sets ......................................................... 3-10
Results Sets: Cursor Mode........................................................................................ 3-10
Result Sets: Sequential Mode ................................................................................... 3-10
Data Dictionary Translations ................................................................................................. 3-11
Date-Time Data Types............................................................................................................. 3-12
Two-Phase Commit Protocol ................................................................................................. 3-13
Piecewise LONG Data Type................................................................................................... 3-13
SQL*Plus DESCRIBE Command ........................................................................................... 3-13
Constraints on SQL in a Distributed Environment............................................................. 3-13
Remote and Heterogeneous References ........................................................................ 3-14
Important Restrictions ..................................................................................................... 3-14
Oracle's Optimizer and Heterogeneous Services ................................................................ 3-17
Example: Using Index and Table Statistics ................................................................... 3-18
Example: Remote Join Optimization.............................................................................. 3-19
Optimizer Restrictions for Non-Oracle Access ............................................................ 3-20
Using Heterogeneous Services Agents
4.1
4.1.1
4.1.1.1
4.1.2
4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.3
4.4
4.4.1
4.4.1.1
4.4.1.2
4.4.1.3
4.4.2
iv
Data Dictionary Views ........................................................................................................ 2-6
Gateway Process Flow ............................................................................................................... 2-6
Initialization Parameters ............................................................................................................
Encrypting Initialization Parameters ................................................................................
Using the dg4pwd Utility............................................................................................
Gateway Initialization Parameters ....................................................................................
Optimizing Data Transfers Using Bulk Fetch.........................................................................
Using OCI, an Oracle Precompiler, or Another Tool for Array Fetches......................
Controlling the Array Fetch Between Oracle Database and the Agent ......................
Controlling the Array Fetch Between the Agent and the Non-Oracle System...........
Controlling the Reblocking of Array Fetches ..................................................................
Optimizing Data Loads Using Parallel Load..........................................................................
Registering Agents......................................................................................................................
Enabling Agent Self-Registration ......................................................................................
Using Agent Self-Registration to Avoid Configuration Mismatches ...................
Understanding Agent Self-Registration ....................................................................
Specifying HS_AUTOREGISTER ...............................................................................
Disabling Agent Self-Registration .....................................................................................
4-1
4-2
4-2
4-3
4-3
4-4
4-4
4-4
4-5
4-5
4-5
4-6
4-6
4-7
4-8
4-8
4.5
Oracle Database Server SQL Construct Processing ............................................................... 4-9
4.5.1
Data Type Checking Support for a Remote-Mapped Statement ............................... 4-10
4.6
Executing User-Defined Functions on a Non-Oracle Database ........................................ 4-10
4.7
Using Synonyms ...................................................................................................................... 4-11
4.7.1
Example of a Distributed Query..................................................................................... 4-12
4.8
Copying Data from the Oracle Database Server to the Non-Oracle Database System.. 4-12
4.9
Copying Data from the Non-Oracle Database System to the Oracle Database Server.. 4-13
4.10
Using Heterogeneous Services Data Dictionary Views ..................................................... 4-14
4.10.1
Understanding the Types of Views................................................................................ 4-14
4.10.2
Understanding the Sources of Data Dictionary Information ..................................... 4-15
4.10.3
Using the General Views ................................................................................................. 4-15
4.10.4
Using the Transaction Service Views............................................................................. 4-16
4.10.5
Using the SQL Service Views.......................................................................................... 4-17
4.10.5.1
Using Views for Capabilities and Translations..................................................... 4-17
4.10.5.2
Using Views for Data Dictionary Translations ..................................................... 4-17
4.11
Using the Heterogeneous Services Dynamic Performance Views ................................... 4-18
4.11.1
Determining Which Agents Are Running on a Host: V$HS_AGENT View ........... 4-18
4.11.2
Determining the Open Heterogeneous Services Sessions:
V$HS_SESSION View ...................................................................................................... 4-18
4.11.3
Determining the Heterogeneous Services Parameters:
V$HS_PARAMETER View.............................................................................................. 4-19
5
Performance Recommendations
5.1
5.2
Optimizing Heterogeneous Distributed SQL Statements..................................................... 5-1
Optimizing Performance of Distributed Queries................................................................... 5-1
Index
v
List of Figures
2–1
2–2
2–3
3–1
3–2
4–1
vi
Oracle Heterogeneous Connectivity Process Architecture...................................................
Accessing Multiple Non-Oracle Instances ..............................................................................
Gateway Process Flow ...............................................................................................................
Flow Diagram for Nonquery Passthrough SQL.....................................................................
Passthrough SQL for Queries....................................................................................................
Optimizing Data Transfers ........................................................................................................
2-1
2-5
2-6
3-6
3-8
4-4
List of Tables
4–1
4–2
4–3
4–4
Data Dictionary Views for Heterogeneous Services..........................................................
Important Columns in the V$HS_AGENT View ...............................................................
Important Columns in the V$HS_SESSION View .............................................................
Important Columns in the V$HS_SESSION View .............................................................
4-14
4-18
4-18
4-19
vii
viii
Preface
This guide describes Oracle's approach for information integration in a heterogeneous
environment. Specifically, it describes Oracle Database gateways.
This preface contains these topics:
■
Audience
■
Documentation Accessibility
■
Related Documents
■
Conventions
Audience
This guide is intended for the following users:
■
■
■
Database administrators who want to manage distributed database systems that
involve Oracle to non-Oracle database links
Application developers who want to use the heterogeneous connectivity
functionality in Oracle database
Readers who want a high-level understanding of Oracle's architecture for
heterogeneous connectivity and how it works
To use this guide, you must be familiar with relational database concepts and basic
database or applications administration. You must be familiar with the operating
system environment under which database administrators are running Oracle
software.
Documentation Accessibility
Our goal is to make Oracle products, services, and supporting documentation
accessible to all users, including users that are disabled. To that end, our
documentation includes features that make information available to users of assistive
technology. This documentation is available in HTML format, and contains markup to
facilitate access by the disabled community. Accessibility standards will continue to
evolve over time, and Oracle is actively engaged with other market-leading
technology vendors to address technical obstacles so that our documentation can be
accessible to all of our customers. For more information, visit the Oracle Accessibility
Program Web site at http://www.oracle.com/accessibility/.
ix
Accessibility of Code Examples in Documentation
Screen readers may not always correctly read the code examples in this document. The
conventions for writing code require that closing braces should appear on an
otherwise empty line; however, some screen readers may not always read a line of text
that consists solely of a bracket or brace.
Accessibility of Links to External Web Sites in Documentation
This documentation may contain links to Web sites of other companies or
organizations that Oracle does not own or control. Oracle neither evaluates nor makes
any representations regarding the accessibility of these Web sites.
Deaf/Hard of Hearing Access to Oracle Support Services
To reach Oracle Support Services, use a telecommunications relay service (TRS) to call
Oracle Support at 1.800.223.1711. An Oracle Support Services engineer will handle
technical issues and provide customer support according to the Oracle service request
process. Information about TRS is available at
http://www.fcc.gov/cgb/consumerfacts/trs.html, and a list of phone
numbers is available at http://www.fcc.gov/cgb/dro/trsphonebk.html.
Related Documents
For more information, see the following:
■
Oracle Database Concepts
■
Oracle Database Administrator's Guide
■
Oracle Database Advanced Application Developer's Guide
Many of the examples in this guide use the sample schemas, which are installed by
default when you select the Basic Installation option with an Oracle Database
installation. See Oracle Database Sample Schemas for information about how these
schemas were created and how to use them.
Conventions
The following text conventions are used in this document:
x
Convention
Meaning
boldface
Boldface type indicates graphical user interface elements associated
with an action, or terms defined in text or the glossary.
italic
Italic type indicates book titles, emphasis, or placeholder variables for
which you supply particular values.
monospace
Monospace type indicates commands within a paragraph, URLs, code
in examples, text that appears on the screen, or text that you enter.
What's New in Heterogeneous Connectivity
User's Guide?
This section describes new features of the Oracle Database 11g Release 2 (11.2) and
provides pointers to additional information. New features information from previous
releases is retained to help those users migrating to the current release.
The following sections describe the new features in Oracle Database Heterogeneous
Connectivity User's Guide:
■
Oracle Database 11g Release 2 (11.2) New Features
■
Oracle Database 11g Release 1 (11.1) New Features
Oracle Database 11g Release 2 (11.2) New Features
New features for Oracle Database 11g Release 2 (11.2) in the Oracle Database
Heterogeneous Connectivity User's Guide include:
■
Gateway CHAR Semantics
This feature allows any HS-based gateway to optionally run in CHAR Semantics
mode. Rather than always describing non-Oracle database columns as CHAR(n
BYTE), this new feature describes them as CHAR(n CHAR) and VARCHAR(n
CHAR). The concept is similar to Oracle Database CHAR Semantics.
■
Multi-byte character sets ratio suppression
This feature optionally suppresses the ratio expansion from the non-Oracle
database involving multi-byte character set (for example, from US7ASCII to
AL32UTF8, or from KO16MSWIN949 to KO16KSC5601). By default, Oracle
Gateways assume the worst ratio to prevent data being truncated or insufficient
buffer size situation.
■
IPv6
This release fully supports IPv6 between Oracle Database and Oracle Database
gateways. For some gateways, IPv6 is also supported between Oracle Database
gateways and the non-Oracle targets.
■
Gateway IDLE timeout
This release allows some Gateways to specify a session idle timeout limit. When a
gateway session is idle for more than the specified time limit, the gateway session
is terminated automatically with any pending update rolled back (if the gateway
has the proper rollback capability).
xi
See Also: For additional information, consult the Oracle
documentation for that specific gateway
Oracle Database 11g Release 1 (11.1) New Features
New features for Oracle Database 11g Release 1 (11.1) in the Oracle Database
Heterogeneous Connectivity User's Guide include:
■
Parallel data retrieval
The Heterogeneous Services agent architecture was enhanced for parallel data
retrieval from remote non-Oracle databases. With this feature, gateway customers
experience improved elapsed time for data retrieval and load.
This feature includes the new DBMS_HS_PARALLEL package. Four new
procedures are introduced with this package:
–
LOAD_TABLE
This procedure loads the data from a remote table to a local Oracle table in
parallel. If the local Oracle table does not already exist, it is created
automatically.
–
CREATE_TABLE_TEMPLATE
This procedure writes out a CREATE TABLE template based on information
gathered from the remote table. You can use the information to add any
optimal Oracle CREATE TABLE clauses.
–
CREATE_OR_REPLACE_VIEW
This procedure creates (or replaces) a read-only view to be referenced for
retrieving the data from a remote table in parallel.
–
DROP_VIEW
This procedure drops the view and internal objects created by the CREATE_
OR_REPLACE_VIEW procedure. If the view has not already been created by
the CREATE_OR_REPLACE_VIEW procedure, an error message is returned.
See Also:
■
Oracle Database PL/SQL Packages and Types Reference
Optimizer interface improvements
The statistics interface of Heterogeneous Services was enhanced to enable the
Oracle optimizer to derive an equivalent execution plan for distributed SQL when
dealing with a remote Oracle database and the agent. With this feature, customers
experience similar or better elapsed time for distributed SQL across the gateways.
xii
1
Introduction
This chapter describes the challenges of operating in a heterogeneous environment.
Oracle recognizes these challenges and offers both synchronous and asynchronous
solutions that enable companies to easily operate in such an environment. The
synchronous solution, Oracle Database gateway, is discussed in this guide.
This chapter contains the following topics:
■
The Information Integration Challenge
■
How Oracle Addresses Synchronous Information Integration
■
Benefits of Oracle's Solution for Synchronous Information Integration
See Also: For information about a specific Oracle Database
gateway, consult the Oracle documentation for that specific
gateway
1.1 The Information Integration Challenge
Information integration is a challenge that affects many organizations because they
may run several different database systems. Each of these systems store data and has a
set of applications that run against the data. This data is just bits and bytes on a file
system - and only a database can turn the bits and bytes of data into business
information. Integration and consolidation of all business information allows an
organization to take advantage of the synergies inherent in business information.
Consolidation of all data into one database system is often difficult. This is primarily
because many of the applications that run against one database may not have an
equivalent application that runs against another. Until migrating data to one
consolidated database system is possible, the heterogeneous database systems must
work together.
There are several problems to overcome before interoperability is possible. The
database systems can be accessed using different interfaces, different data types,
different capabilities, and different ways of handling errors. Even when one relational
database tries to access another relational database, the differences are significant. In
this situation, the common features of the databases include data access through SQL,
two-phase commit protocol, and similar data types.
There are also significant differences. SQL dialects can be different, as can transaction
semantics. There can be some data types in one database that do not exist in the other.
The most significant area of difference is in the data dictionaries of the two databases.
Most data dictionaries contain similar information, but the information is structured
for each data dictionary in a different way. There are several ways of overcoming this
Introduction 1-1
How Oracle Addresses Synchronous Information Integration
problem. This guide describes Oracle’s approach to synchronously access information
from multiple sources.
1.2 How Oracle Addresses Synchronous Information Integration
If a client program must access or modify data on several Oracle databases, it can open
connections to each of them. This approach, however, has several drawbacks; among
them are the following:
■
To join data from the databases, the client must have logic allowing that.
■
To guarantee data integrit, the client must have transaction coordination logic.
Oracle provides another approach called distributed processing, where the client
connects to one Oracle database and shifts the burden of joining data and transaction
coordination to that database. The database to which the client program connects is
called the local database. Any database other than this one is a remote database. The
client program can access objects at any of the remote databases using database links.
The Oracle query processor takes care of the joins and its transaction engine takes care
of the transaction coordination.
The approach that Oracle took to solve the heterogeneous connectivity problem is to
allow a non-Oracle system to be one of the remote nodes in the previously described
scenario. The remote non-Oracle system functions as a remote Oracle system. The
non-Oracle system uses the same SQL dialect and the same data dictionary structure
as an Oracle system. Access to a non-Oracle system is done through Heterogeneous
Services.
The work done by the Heterogeneous Services component is, for the most part,
completely transparent to the end user. With only a few exceptions (these are noted in
later chapters), you are not required to do anything different to access a non-Oracle
system than is required for accessing an Oracle system. The Heterogeneous Services
component is used as the foundation for implementing Oracle's access to non-Oracle
databases.
An Oracle Database gateway works in conjunction with the Heterogeneous Services
component of Oracle Database to access a particular, commercially available,
non-Oracle system for which that Oracle Database gateway was designed. For
example, you use the Oracle Database Gateway for Sybase to access a Sybase database.
Oracle also provides an Oracle Database Gateway for ODBC which enables you to use
ODBC drivers to access non-Oracle databases.
Using an Oracle Database gateway, you can access data anywhere in a distributed
database system without being required to know either the location of the data or how
it is stored.
The ODBC drivers that are required by Oracle Database
Gateway for ODBC are not supplied by Oracle. Users must obtain
drivers from other vendors.
Note:
Oracle also offers asynchronous information integration products. Those products are
not discussed in this guide. Briefly, these products include:
■
Oracle Streams
Oracle Streams enables the propagation of data, transactions, and events in a
single data stream or queue, either within a database or among multiple
databases. Not only can Oracle Streams capture, propagate, and apply changes to
1-2 Oracle Database Heterogeneous Connectivity User's Guide
Benefits of Oracle's Solution for Synchronous Information Integration
data, it can also handle data structure changes (DDL) and user-defined events.
Changes can be captured and applied as is, or transformed at any point in the
capture, propagation, and application processing.
■
Messaging Gateway
The Messaging Gateway enables communication between Oracle Database and
non-Oracle messaging systems.
■
Open System Interfaces
Oracle offers a number of open interfaces, such as OCI, JDBC, and ODBC, that
enable customers to use third-party applications or to write their own client
applications to access Oracle Database.
1.3 Benefits of Oracle's Solution for Synchronous Information Integration
Much of the processing power of Oracle Database gateways is integrated into the
database. This provides an efficient solution for information integration that enables
full exploitation of the power and features of the Oracle database. This includes such
features as powerful SQL parsing and distributed optimization capabilities.
The following sections describe the benefits of Oracle's approach to resolving the
challenges of a heterogeneous environment:
■
Remote Data Can Be Accessed Transparently
■
No Unnecessary Data Duplication
■
SQL Statements Can Query Several Different Databases
■
Oracle's Application Development and End User Tools Can Be Used
■
Users Can Communicate With a Remote Database in its Own Language
1.3.1 Remote Data Can Be Accessed Transparently
Oracle Database gateways provide the ability to transparently access data in
non-Oracle databases from an Oracle environment. You can create synonyms for the
objects in a non-Oracle database and refer to them without having to specify a physical
location. This transparency eliminates the need for application developers to
customize their applications to access data from different non-Oracle systems, thus
decreasing development efforts and increasing the mobility of the application.
Instead of requiring applications to interoperate with non-Oracle systems using their
native interfaces (which can result in intensive application-side processing),
applications can be built upon a consistent Oracle interface for both Oracle and
non-Oracle systems.
1.3.2 No Unnecessary Data Duplication
Oracle Database gateways provide applications direct access to data in non-Oracle
databases. This eliminates the need to upload and download large amounts of data to
different locations, thus reducing data duplication and saving disk storage space. By
eliminating uploading and downloading large amounts of data, there is a reduced
risk for unsynchronized or inconsistent data.
Introduction 1-3
Benefits of Oracle's Solution for Synchronous Information Integration
1.3.3 SQL Statements Can Query Several Different Databases
An Oracle database accepts SQL statements that query data stored in several different
databases. An Oracle database with the Heterogeneous Services component processes
the SQL statement and passes the appropriate SQL code directly to other Oracle
databases and through gateways to non-Oracle databases. The Oracle database
combines the results and returns them to the client.
1.3.4 Oracle's Application Development and End User Tools Can Be Used
Oracle Database gateways extend the range of Oracle's database and application
development tools. Oracle has tools that increase application development and user
productivity by reducing prototype, development, and maintenance time.
You are not required to develop new tools or learn how to use other tools to access
data stored in non-Oracle databases. Instead, you can access Oracle and non-Oracle
data with a single set of Oracle tools. These tools can run on remote systems connected
through Oracle Net to an Oracle database.
1.3.5 Users Can Communicate With a Remote Database in its Own Language
Oracle enables you to transparently access non-Oracle systems using SQL statements.
In some cases, however, it becomes necessary to use non-Oracle system SQL to access
the non-Oracle system. For such cases, Heterogeneous Services has a passthrough
feature that enables you to bypass Oracle's query processor and to communicate with
the remote database in its own language.
1-4 Oracle Database Heterogeneous Connectivity User's Guide
2
The Role of the Heterogeneous Services
Component
Oracle's synchronous solutions for operating in a heterogeneous environment are
Oracle Database gateways. The common component of Oracle Database for
supporting these solutions is Heterogeneous Services. This chapter describes the
architecture and functionality of the Heterogeneous Services component and its
interaction with Oracle Database gateways.
This chapter contains the following topics:
■
Heterogeneous Connectivity Process Architecture
■
Heterogeneous Services Agents
■
Types of Heterogeneous Services Agents
■
Heterogeneous Services Components
■
Heterogeneous Services Configuration Information
■
The Heterogeneous Services Data Dictionary
■
Gateway Process Flow
2.1 Heterogeneous Connectivity Process Architecture
At a high level, Oracle heterogeneous connectivity process architecture is structured as
shown in Figure 2–1.
Figure 2–1 Oracle Heterogeneous Connectivity Process Architecture
Agent
Oracle
Heterogenous
Service
Agent
Generic
Code
Driver
Remote
Database
The Heterogeneous Services component in Oracle Database communicates with a
Heterogeneous Services agent process which, in turn, communicates with the
non-Oracle system. The code can be conceptually divided into three parts:
■
The Heterogeneous Services component in Oracle Database
This module performs most of the processing related to heterogeneous
connectivity.
The Role of the Heterogeneous Services Component
2-1
Heterogeneous Services Agents
■
Agent generic code
This is code in the agent that is generic to all Heterogeneous Services products.
This code communicates with the database and provides multithreading support.
■
The driver
This module communicates with the non-Oracle system. It is used to map calls
from the Heterogeneous Services to the native API of the non-Oracle system, and
it is not specific to Oracle systems.
2.2 Heterogeneous Services Agents
A Heterogeneous Services agent is the process through which Oracle Database
connects to a non-Oracle system. The agent process that accesses a non-Oracle system
is called a gateway. Access to all gateways goes through the Heterogeneous Services
component in Oracle Database and all gateways contain the same agent-generic code.
Each gateway has a different driver linked in that maps the Heterogeneous Services to
the client API of the non-Oracle system.
The agent process consists of two components. These are agent generic code and a
non-Oracle system-specific driver. An agent exists primarily to isolate Oracle Database
from third-party code. For a process to access the non-Oracle system, the non-Oracle
system client libraries must be linked into it. In the absence of the agent process, these
libraries would have to be directly linked into the Oracle database and problems in
this code could cause Oracle Database to fail. An agent process isolates Oracle
Database from any problems in third-party code. Even if a fatal error occurs in the
thirde-party code, only the agent process will end.
An agent can be in the following places:
■
On the same computer as the non-Oracle system
■
On the same computer as Oracle Database
■
On a computer different from either of these two
Agent processes are started when a user session accesses a non-Oracle system through
a database link. These connections are made using Oracle's remote data access
software, Oracle Net Services, which enables both client/server and server/server
communication. The agent process continues to run until the user session is
disconnected or the database link is explicitly closed.
Multithreaded agents act differently. They must be explicitly started and shut down
by a database administrator, instead of automatically being spawned by Oracle Net
Services
2.3 Types of Heterogeneous Services Agents
There are two types of Heterogeneous Services agents:
■
Oracle Database Gateways
■
Oracle Database Gateway for ODBC Agent
2.3.1 Oracle Database Gateways
An Oracle Database gateway is a gateway that is designed for accessing a specific
non-Oracle system. Oracle provides gateways to access several commercially available
non-Oracle systems. For example, an Oracle Database Gateway for Sybase is designed
to access Sybase databases.
2-2 Oracle Database Heterogeneous Connectivity User's Guide
Heterogeneous Services Components
With Oracle Database gateways, you can access data anywhere in a distributed
database system without being required to know either the location of the data or how
it is stored. When the results of your queries are returned to you by Oracle Database,
they are presented to you as if the data stores from which they were taken all resided
within a remote instance of an Oracle distributed database.
2.3.2 Oracle Database Gateway for ODBC Agent
In addition to Oracle Database gateways for various non-Oracle database systems,
there is the Oracle Database Gateway for ODBC agent. This agent contains only
generic code, and the customer is responsible for providing the necessary drivers.
Oracle Database Gateway for ODBC enables you to use ODBC drivers to access
non-Oracle systems that have an ODBC interface.
To access a specific non-Oracle system using Oracle Database Gateway for ODBC, you
must configure an ODBC driver to the non-Oracle system. These drivers are not
provided by Oracle. However, if the non-Oracle system supports the ODBC protocols,
you can use Oracle Database Gateway for ODBC to access any non-Oracle system that
can be accessed using an ODBC driver.
Oracle Database Gateway for ODBC has some limitations. Especially, when compared
to a paticular target, the functionality and performance are limited.
2.4 Heterogeneous Services Components
This section discusses the components of Heterogeneous Services in Oracle Database.
These components are:
■
Transaction Service
■
SQL Service
2.4.1 Transaction Service
The transaction service component of the Heterogeneous Services component enables
non-Oracle systems to be integrated into Oracle Database transactions and sessions.
When you access a non-Oracle system for the first time using a database link within
your Oracle user session, you transparently set up an authenticated session in the
non-Oracle system. At the end of your Oracle user session, the authenticated session in
the non-Oracle database system is closed.
Additionally, one or more non-Oracle systems can participate in an Oracle distributed
transaction. When an application commits a transaction, Oracle's two-phase commit
protocol accesses the non-Oracle database system to transparently coordinate the
distributed transaction. Even in those cases where the non-Oracle system does not
support all aspects of Oracle two-phase commit protocol, Oracle can (with some
limitations) support distributed transactions with the non-Oracle system.
2.4.2 SQL Service
The structured query language (SQL) service handles the processing of all SQL-related
operations. The work done by the SQL service includes:
■
Mapping Oracle internal SQL-related calls to the Heterogeneous Services driver
application programing interface (API). This API is then mapped by the driver to
the client API of the non-Oracle system.
The Role of the Heterogeneous Services Component
2-3
Heterogeneous Services Configuration Information
■
■
■
■
Translating SQL statements from Oracle's SQL dialect to the SQL dialect of the
non-Oracle system.
Translating queries that reference Oracle data dictionary tables to queries that
extract the necessary information from the non-Oracle system’s data dictionary.
Converting data from non-Oracle system data types to Oracle data types and back.
Compensating for missing functionality of the non-Oracle system by issuing
multiple queries to get the necessary data and doing postprocessing to get the
desired results.
2.5 Heterogeneous Services Configuration Information
Heterogeneous Services components consist of generic code and must be configured to
work with many different non-Oracle systems. Each gateway has configuration
information stored in the driver module. The information is uploaded to the server
immediately after the connection to the gateway is established. The configuration
information includes:
■
Data Dictionary Translation Views
■
Heterogeneous Services Initialization Parameters
■
Capabilities
2.5.1 Data Dictionary Translation Views
Data dictionary translations are views on non-Oracle data dictionary tables. They help
Heterogeneous Services translate references to Oracle data dictionary tables into
queries that can retrieve the equivalent information from the non-Oracle data
dictionary.
2.5.2 Heterogeneous Services Initialization Parameters
Heterogeneous Services initialization parameters serve two functions:
■
■
They give you a means of fine-tuning the gateway to optimize performance and
memory utilization for the gateway and the Heterogeneous Services component.
They enable you to inform the gateway (and, thereby, Heterogeneous Services)
how the non-Oracle system was configured (for example, in what language the
non-Oracle system is running). They give information to Heterogeneous Services
about the configurable properties of the non-Oracle system.
You can examine the Heterogeneous Services initialization parameters for a session by
querying the view V$HS_PARAMETER. Users can set initialization parameters in
gateway initialization files.
2.5.3 Capabilities
Capabilities tell Heterogeneous Services about the limitations of the non-Oracle system
(such as what types of SQL statements are supported) and how to map Oracle data
types and SQL expressions to their non-Oracle system equivalents. In other words,
they tell Heterogeneous Services about the non-configurable properties of the
non-Oracle system. Capabilities cannot be changed by the user.
2-4 Oracle Database Heterogeneous Connectivity User's Guide
The Heterogeneous Services Data Dictionary
2.6 The Heterogeneous Services Data Dictionary
Configuration information is uploaded from an agent to the Heterogeneous Services
component immediately after the connection to the agent is established. The
configuration information is stored in Heterogeneous Services data dictionary tables.
No further uploading occurs until something at the agent changes (for example, if a
patch is applied or if the agent is upgraded to a new version).
The following sections describe:
■
Classes and Instances
■
Data Dictionary Views
2.6.1 Classes and Instances
Using Heterogeneous Services, you can access several non-Oracle systems from a
single Oracle database. This is illustrated in Figure 2–2, which shows two non-Oracle
systems being accessed.
Figure 2–2 Accessing Multiple Non-Oracle Instances
Client Application
Agent
Oracle Server
Non-Oracle System &quot;X&quot;
instance
Agent
Non-Oracle System &quot;Y&quot;
instance
Both agents upload configuration information, which is stored as part of the
Heterogeneous Services data dictionary information on Oracle Database.
Although it is possible to store data dictionary information at one level of granularity
by having completely separate definitions in the Heterogeneous Services data
dictionary for each individual instance, this can lead to an unnecessarily large amount
of redundant data dictionary information. To avoid this, Oracle organizes the
Heterogeneous Services data dictionary by two levels of granularity, called class and
instance.
A class pertains to a specific type of non-Oracle system. For example, you may want to
access the class of Sybase database systems with Oracle Database. An instance defines
specializations within a class. For example, you may want to access several separate
instances within a Sybase database system. Each class definition (one level of
granularity) is shared by all the particular instances (a second level of granularity)
under that class. Further, instance information takes precedence over class
information, and class information takes precedence over server-supplied defaults.
For example, suppose that Oracle Database accesses three instances of Sybase and two
instances of Ingres II. Sybase and Ingres II each have their own code, requiring
separate class definitions for Oracle Database to access them. The Heterogeneous
Services data dictionary therefore would contain two class definitions, one for Sybase
The Role of the Heterogeneous Services Component
2-5
Gateway Process Flow
and one for Ingres II, with five instance definitions, one for each instance being
accessed by Oracle Database.
Note that instance-level capability and data dictionary information are session-specific
and are not stored in the Heterogeneous Services data dictionary of Oracle Database.
However, instance-level initialization parameters can be stored in the database.
2.6.2 Data Dictionary Views
The Heterogeneous Services data dictionary views contain the following kinds of
information:
■
Names of instances and classes uploaded into the Oracle data dictionary
■
Capabilities, including SQL translations, defined for each class or instance
■
Data Dictionary translations defined for each class or instance
■
Initialization parameters defined for each class or instance
You can access information from the Oracle data dictionary by using fixed views. The
views are categorized into three main types:
■
General views
■
Views used for the transaction service
■
Views used for the SQL service
2.7 Gateway Process Flow
Figure 2–3 shows a typical gateway process flow. The steps explain the sequence of
events that occur when a client application queries the non-Oracle database system
database through the gateway.
Figure 2–3 Gateway Process Flow
1
8
1.
4
Oracle
Net
7
Oracle
Net
6
3
5
Non-Oracle System
2
Gateway
Heterogeneous Services
Oracle Server
Oracle Net
The client application sends a query using Oracle Net to Oracle Database.
2-6 Oracle Database Heterogeneous Connectivity User's Guide
Gateway Process Flow
2.
Heterogeneous Services and the gateway converts the SQL statement into a SQL
statement understood by the non-Oracle database system.
3.
Oracle Database sends the query to the gateway using Oracle Net.
4.
For the first transaction in a session, the gateway logs in to non-Oracle database
system using a user name and password that is valid in the non-Oracle system.
5.
The gateway retrieves data using non-Oracle database system SQL statements.
6.
The gateway converts retrieved data into a format compatible with Oracle
Database.
7.
The gateway returns query results to Oracle Database, again using Oracle Net
Services.
8.
Oracle Database passes the query results to the client application using Oracle Net.
The database link remains open until the gateway session is finished, or the
database link is explicitly closed.
The Role of the Heterogeneous Services Component
2-7
Gateway Process Flow
2-8 Oracle Database Heterogeneous Connectivity User's Guide
3
Features of Oracle Database Gateways
This chapter describes the major features provided by Oracle Database gateways.
Descriptions of these features are in the following topics:
■
SQL and PL/SQL Support
■
Heterogeneous Replication
■
Passthrough SQL
■
Result Set Support
■
Data Dictionary Translations
■
Date-Time Data Types
■
Two-Phase Commit Protocol
■
Piecewise LONG Data Type
■
SQL*Plus DESCRIBE Command
■
Constraints on SQL in a Distributed Environment
■
Oracle's Optimizer and Heterogeneous Services
These features may not be available in all Heterogeneous
Services gateways. Not only must there be generic support for these
features, which Heterogeneous Services provides, but there must
also be support added to the driver for them. Consult the
appropriate gateway documentation to determine if a particular
feature is supported for your gateway.
Note:
3.1 SQL and PL/SQL Support
SQL statements are translated and data types are mapped according to capabilities.
PL/SQL calls are mapped to non-Oracle system stored procedures. With SQL
statements, if functionality is missing at the remote system, then either a simpler query
is issued or the statement is broken up into multiple queries. Then, the desired results
are obtained by postprocessing in the Oracle database.
Even though Heterogeneous Services can, for the most part, incorporate non-Oracle
systems into Oracle distributed sessions, there are several limitations to this. Some of
the generic limitations are:
■
There is no support for CONNECT BY clauses in SQL statements.
Features of Oracle Database Gateways 3-1
Heterogeneous Replication
■
■
■
■
■
ROWID support is limited; consult individual gateway documentation for more
details. The Oracle Universal ROWID data type is not supported in any gateway
that uses Heterogeneous Services.
Large objects (LOBs), abstract data types (ADTs), and reference data types (REFs)
are not supported.
Remote packages are not supported.
Remote stored procedures can have out arguments of type REF CURSOR but not
in or in-out objects.
Oracle Heterogeneous Services agents do not support shared database links.
In addition to these generic limitations, each gateway can
have additional limitations. See the gateway documentation for
individual gateways for a complete list of limitations of the
product.
Note:
3.2 Heterogeneous Replication
Data can be replicated between a non-Oracle system and Oracle Database using
materialized views.
There is another means of replicating information between
Oracle and non-Oracle databases called Oracle Streams.
Note:
For information about using Oracle Streams, see Oracle Streams
Concepts and Administration.
Materialized views instantiate data captured from tables at the non-Oracle master site
at a particular time. This instant is defined by a refresh operation, which copies this
data to Oracle Database and synchronizes the copy on the Oracle system with the
master copy on the non-Oracle system. The materialized data is then available as a
view on Oracle Database.
Replication facilities provide mechanisms to schedule refreshes and to collect
materialized views into replication groups to facilitate their administration. Refresh
groups permit refreshing multiple materialized views as if they were a single object.
Heterogeneous replication support is necessarily limited to a subset of the full
Oracle-to-Oracle replication functionality:
■
■
■
Only the non-Oracle system can be the primary site. This is because materialized
views can be created only on Oracle Database.
Materialized views must use a complete refresh. This is because fast refresh would
require Oracle-specific functionality in the non-Oracle system.
Not all types of materialized views can be created to reference tables on a
non-Oracle system. Primary key and subquery materialized views are supported,
but ROWID and OBJECT ID materialized views are not supported. This is because
there is no SQL standard for the format and contents of ROWID, and non-Oracle
systems do not implement Oracle objects.
Other restrictions apply to any access to non-Oracle data through Oracle's
Heterogeneous Services facilities. The most important of these are:
3-2 Oracle Database Heterogeneous Connectivity User's Guide
Heterogeneous Replication
■
■
Non-Oracle data types in table columns mapped to a fixed view must be
compatible with (that is, have a mapping to or from) Oracle data types. This is
usually true for data types defined by ANSI SQL standards.
A subquery materialized view may not be able to use language features restricted
by individual non-Oracle systems. In many cases, Heterogeneous Services
supports such language features by processing queries within Oracle Database.
Occasionally the non-Oracle systems impose limitations that cannot be detected
until Heterogeneous Services attempts to execute the query.
The following examples illustrate basic setup and use of three materialized views to
replicate data from a non-Oracle system to an Oracle data store.
For the following examples, remote_db refers to the
non-Oracle system that you are accessing from Oracle Database.
Note:
Modify these examples for your environment. Do not try to execute
them as they are written.
Example 1: Create Materialized Views for Heterogeneous Replication
This example creates three materialized views that are then used in subsequent
examples.
1.
Create a primary key materialized view of table customer@remote_db.
CREATE MATERIALIZED VIEW pk_mv REFRESH COMPLETE AS
SELECT * FROM customer@remote_db WHERE &quot;zip&quot; = 94555;
2.
Create a subquery materialized view of tables orders@remote_db and
customer@remote_db.
CREATE MATERIALIZED VIEW sq_mv REFRESH COMPLETE AS
SELECT * FROM orders@remote_db o WHERE EXISTS
(SELECT c.&quot;c_id&quot; FROM customer@remote_db c
WHERE c.&quot;zip&quot; = 94555 and c.&quot;c_id&quot; = o.&quot;c_id&quot; );
3.
Create a complex materialized view of data from multiple tables on remote_db.
CREATE MATERIALIZED VIEW cx_mv
REFRESH COMPLETE AS
SELECT c.&quot;c_id&quot;, o.&quot;o_id&quot;
FROM customer@remote_db c,
orders@remote_db o,
order_line@remote_db ol
WHERE c.&quot;c_id&quot; = o.&quot;c_id&quot;
AND o.&quot;o_id&quot; = ol.&quot;o_id&quot;;
Example 2: Set Up a Refresh Group for Heterogeneous Replication
BEGIN
dbms_refresh.make('refgroup1',
'pk_mv, sq_mv, cx_mv',
NULL, NULL);
END;
/
Example 3: Force Refresh of All Three Materialized Views
BEGIN
dbms_refresh.refresh('refgroup1');
Features of Oracle Database Gateways 3-3
Passthrough SQL
END;
/
See Also: Oracle Database Advanced Replication for a complete
description of materialized views and replication facilities
3.3 Passthrough SQL
The passthrough SQL feature enables you to send a statement directly to a non-Oracle
system without first being interpreted by Oracle Database. This feature can be useful if
the non-Oracle system allows for operations in statements for which there is no
equivalent in Oracle.
This section contains the following topics:
■
Using the DBMS_HS_PASSTHROUGH Package
■
Considering the Implications of Using Passthrough SQL
■
Executing Passthrough SQL Statements
3.3.1 Using the DBMS_HS_PASSTHROUGH Package
You can execute passthrough SQL statements directly on the non-Oracle system using
the PL/SQL package DBMS_HS_PASSTHROUGH. Any statement executed with this
package is executed in the same transaction as standard SQL statements.
The DBMS_HS_PASSTHROUGH package is a virtual package. It conceptually resides on
the non-Oracle system. In reality, however, calls to this package are intercepted by
Heterogeneous Services and are mapped to one or more Heterogeneous Services calls.
The driver then maps these Heterogeneous Services calls to the API of the non-Oracle
system. The client application invokes the procedures in the package through a
database link in the same way as it would invoke a non-Oracle system stored
procedure. The special processing done by Heterogeneous Services is transparent to
the user.
Oracle Database PL/SQL Packages and Types Reference for
more information about this package
See Also:
3.3.2 Considering the Implications of Using Passthrough SQL
When you execute a passthrough SQL statement that implicitly commits or rolls back a
transaction in a non-Oracle system, the transaction is affected. For example, some
systems implicitly commit the transaction containing a data definition language (DDL)
statement. Because Oracle Database is bypassed, Oracle Database is unaware that a
transaction was committed in the non-Oracle system. Consequently, the data at the
non-Oracle system can be committed, while the transaction in Oracle Database is not.
If the transaction in Oracle Database is rolled back, data inconsistencies between
Oracle Database and the non-Oracle system can occur. This situation results in global
data inconsistency.
Note that if the application executes a typical COMMIT statement, Oracle Database can
coordinate the distributed transaction with the non-Oracle system. The statement
executed with the passthrough facility is part of the distributed transaction.
3-4 Oracle Database Heterogeneous Connectivity User's Guide
Passthrough SQL
3.3.3 Executing Passthrough SQL Statements
The following table shows the functions and procedures provided by the DBMS_HS_
PASSTHROUGH package that enable you to execute passthrough SQL statements.
Procedure/Function
Description
OPEN_CURSOR
Opens a cursor.
CLOSE_CURSOR
Closes a cursor.
PARSE
Parses the statement.
BIND_VARIABLE
Binds IN variables.
BIND_OUT_VARIABLE
Binds OUT variables.
BIND_INOUT_VARIABLE
Binds IN OUT variables.
EXECUTE_NON_QUERY
Executes a nonquery statement.
EXECUTE_IMMEDIATE
Executes a nonquery statement without bind variables.
FETCH_ROW
Fetches rows from query.
GET_VALUE
Retrieves column value from SELECT statement or
retrieves OUT bind parameters.
3.3.3.1 Executing Nonqueries
Nonqueries include the following statements and types of statements:
■
INSERT
■
UPDATE
■
DELETE
■
DDL
To execute nonquery statements, use the EXECUTE_IMMEDIATE function. For
example, to execute a DDL statement on a non-Oracle system that you can access
using the database link salesdb, enter the following:
DECLARE
num_rows INTEGER;
BEGIN
num_rows := DBMS_HS_PASSTHROUGH.EXECUTE_IMMEDIATE@salesdb
('CREATE TABLE dept1 (n SMALLINT, loc CHARACTER(10))');
END;
The variable num_rows is assigned the number of rows affected by the statements that
were executed. For DDL statements, zero is returned. Note that you cannot execute a
query with EXECUTE_IMMEDIATE function and you cannot use bind variables.
3.3.3.1.1 Using Bind Variables: Overview Bind variables let you use the same SQL
statement multiple times with different values, reducing the number of times a SQL
statement needs to be parsed. For example, when you insert four rows in a table, you
can parse the SQL statement once, and bind and execute the SQL statement for each
row. One SQL statement can have zero or more bind variables.
To execute passthrough SQL statements with bind variables, you must:
1.
Open a cursor.
Features of Oracle Database Gateways 3-5
Passthrough SQL
2.
Parse the SQL statement on the non-Oracle system.
3.
Bind the variables.
4.
Execute the SQL statement on the non-Oracle system.
5.
Close the cursor.
Figure 3–1 shows the flow diagram for executing nonqueries with bind variables.
Figure 3–1 Flow Diagram for Nonquery Passthrough SQL
Open
Cursor
Parse
Bind
Variable
(optional)
Execute
non query
Get
Value
(optional)
Close
Cursor
3.3.3.1.2 Using IN Bind Variables The syntax of the non-Oracle system determines how a
statement specifies a bind variable. For example, on an Oracle system you define bind
variables with a preceding colon. For example:
...
UPDATE emp
SET sal=sal*1.1
WHERE ename=:ename;
...
In this statement, ename is the bind variable. On non-Oracle systems, you may need
to specify bind variables with a question mark. For example:
...
UPDATE emp
SET sal=sal*1.1
3-6 Oracle Database Heterogeneous Connectivity User's Guide
Passthrough SQL
WHERE ename= ?;
...
In the bind variable step, you must positionally associate host program variables (in
this case, PL/SQL) with each of these bind variables. For example, to execute the
preceding statement, use the following PL/SQL program:
DECLARE
c INTEGER;
nr INTEGER;
BEGIN
c := DBMS_HS_PASSTHROUGH.OPEN_CURSOR@salesdb;
DBMS_HS_PASSTHROUGH.PARSE@salesdb(c,
'UPDATE emp SET SAL=SAL*1.1 WHERE ename=?');
DBMS_HS_PASSTHROUGH.BIND_VARIABLE@salesdb(c,1,'JONES');
nr:=DBMS_HS_PASSTHROUGH.EXECUTE_NON_QUERY@salesdb(c);
DBMS_OUTPUT.PUT_LINE(nr||' rows updated');
DBMS_HS_PASSTHROUGH.CLOSE_CURSOR@salesdb(c);
END;
3.3.3.1.3 Using OUT Bind Variables The non-Oracle system can support OUT bind
variables. With OUT bind variables, the value of the bind variable is not known until
after the execution of the SQL statement.
Although OUT bind variables are populated after executing the SQL statement, the
non-Oracle system must know that the particular bind variable is an OUT bind variable
before the SQL statement is executed. You must use the BIND_OUT_VARIABLE
procedure to specify that the bind variable is an OUT bind variable.
After executing the SQL statement, you can retrieve the value of the OUT bind variable
using the GET_VALUE procedure.
3.3.3.1.4 Using IN OUT Bind Variables A bind variable can be both an IN and an OUT
variable. This means that the value of the bind variable must be known before
executing the SQL statement, but you can change the value after the SQL statement is
executed.
For IN OUT bind variables, you must use the BIND_INOUT_VARIABLE procedure to
provide a value before executing the SQL statement. After executing the SQL
statement, you must use the GET_VALUE procedure to retrieve the new value of the
bind variable.
3.3.3.2 Executing Queries
The difference between queries and nonqueries is that queries retrieve a result set from
a SELECT statement. The result set is retrieved by using a cursor.
Figure 3–2 illustrates the steps in a passthrough SQL query. After the system parses the
SELECT statement, each row of the result set can be retrieved with the FETCH_ROW
procedure. After the row is retrieved, use the GET_VALUE procedure to retrieve the
selected list of items into program variables. After all rows are retrieved, you can close
the cursor.
Features of Oracle Database Gateways 3-7
Passthrough SQL
Figure 3–2 Passthrough SQL for Queries
Open
Cursor
Parse
Bind
Variable
(optional)
Fetch_row
For each
row
For each
column
Get
Value
Close
Cursor
You do not have to retrieve all the rows. You can close the cursor at any time after
opening the cursor.
Although you are retrieving one row at a time,
Heterogeneous Services optimizes the round-trips between Oracle
Database and the non-Oracle system by buffering multiple rows
and fetching from the non-Oracle data system in one round-trip.
Note:
The following example executes a query:
DECLARE
val VARCHAR2(100);
c
INTEGER;
nr
INTEGER;
BEGIN
c := DBMS_HS_PASSTHROUGH.OPEN_CURSOR@salesdb;
DBMS_HS_PASSTHROUGH.PARSE@salesdb(c,
'select ENAME
from
EMP
where DEPTNO=10');
LOOP
nr := DBMS_HS_PASSTHROUGH.FETCH_ROW@salesdb(c);
EXIT WHEN nr = 0;
DBMS_HS_PASSTHROUGH.GET_VALUE@salesdb(c, 1, val);
3-8 Oracle Database Heterogeneous Connectivity User's Guide
Result Set Support
DBMS_OUTPUT.PUT_LINE(val);
END LOOP;
DBMS_HS_PASSTHROUGH.CLOSE_CURSOR@salesdb(c);
END;
After the SELECT statement has been parsed, the rows are fetched and printed in a
loop until the FETCH_ROW function returns the value 0.
3.4 Result Set Support
Various relational databases enable stored procedures to return result sets (one or
more sets of rows).
Traditionally, database stored procedures worked exactly like procedures in any
high-level programming language. They had a fixed number of arguments which
could be of types IN, OUT, or IN OUT. If a procedure had n arguments, it could return
at most n values as results. However, suppose that you wanted a stored procedure to
execute a query such as SELECT * FROM emp and return the results. The emp table
might have a fixed number of columns, but there is no way of telling, at procedure
creation time, the number of rows it has. Because of this, no traditional stored
procedure could be created that returned the results of this type of query. As a result,
several relational database vendors added the ability to return results sets from stored
procedures, but each relational database returns result sets from stored procedures
differently.
Oracle has a data type called a REF CURSOR. Like every other Oracle data type, a
stored procedure can take this data type as an IN or OUT argument. With Oracle
Database, a stored procedure must have an output argument of type REF CURSOR. It
then opens a cursor for a SQL statement and places a handle to that cursor in that
output parameter. The caller can then retrieve from the REF CURSOR the same way as
from any other cursor.
Oracle Database can do a lot more than return result sets. The REF CURSOR data type
can be passed as an input argument to PL/SQL routines to be passed back and forth
between client programs and PL/SQL routines or as an input argument between
several PL/SQL routines.
This section contains the following topics:
■
Result Set Support for Non-Oracle Systems
■
Heterogeneous Services Support for Result Sets
3.4.1 Result Set Support for Non-Oracle Systems
Several non-Oracle systems allow stored procedures to return result sets, but they do
so in different ways. Result set support for non-Oracle databases is typically based on
one of the following two models.
■
Model 1: Result Set Support
When creating a stored procedure, you can explicitly specify the maximum
number of result sets that can be returned by that stored procedure. While
executing, the stored procedure can open anywhere from zero up to its specified
maximum number of result sets. After the execution of the stored procedure, a
client program gets handles to these result sets by using either an embedded SQL
directive or by calling a client library function. After that, the client program can
retrieve from the result set in the same way as from a typical cursor.
■
Model 2: Result Set Support
Features of Oracle Database Gateways 3-9
Result Set Support
In this model, there is no specified limit to the number of result sets that can be
returned by a stored procedure. Both Model 1 and Oracle Database have a limit.
For Oracle Database, the number of result sets returned by a stored procedure can
be at most the number of REF CURSOR OUT arguments. For Model 1, the upper
limit is specified using a directive in the stored procedure language. Another way
that Model 2 differs from Oracle Database and Model 1 is that they do not return a
handle to the result sets. Instead, they place the entire result set on the wire when
returning from a stored procedure. For Oracle Database, the handle is the REF
CURSOR OUT argument. For Model 1, it is obtained separately after the execution
of the stored procedure. For both Oracle Database and Model 1, after the handle is
obtained, data from the result set is obtained by doing a fetch on the handle; there
are several cursors open and the fetch can be in any order. In the case of Model 2,
however, all the data is already on the wire, with the result sets coming in the
order determined by the stored procedure and the output arguments of the
procedures coming at the end. The entire first result set must be retrieved, then the
entire second result set, until all of the results are retrieved. Finally, the stored
procedure OUT arguments are retrieved.
3.4.2 Heterogeneous Services Support for Result Sets
Result set support exists among non-Oracle databases in different forms. All of these
must be mapped to the Oracle REF CURSOR model. Due to the differences in behavior
among the non-Oracle systems, Heterogeneous Services result set support acts in one
of two different ways depending on the non-Oracle system to which it is connected.
Note the following about Heterogeneous Services result set support:
■
■
■
Result set support is part of the Heterogeneous Services generic code, but for the
feature to work in a gateway, the driver has to implement it. Not all drivers have
implemented result set support and you must verify that your gateway is
supported.
Heterogeneous Services supports REF CURSOR OUT arguments from stored
procedures. IN and IN OUT arguments are not supported.
The REF CURSOR OUT arguments are all anonymous reference cursors. REF
CURSORs that are returned by Heterogeneous Services do not have types.
3.4.2.1 Results Sets: Cursor Mode
Each result set returned by a non-Oracle system stored procedure is mapped by an
Oracle driver to an OUT argument of type REF CURSOR. The client program detects a
stored procedure with several OUT arguments of type REF CURSOR. After executing
the stored procedure, the client program can fetch from the REF CURSOR the same
way as it would from a REF CURSOR returned by an Oracle stored procedure. When
connecting to the gateway as described in Section 3.4.1.1, Heterogeneous Services will
be in cursor mode.
3.4.2.2 Result Sets: Sequential Mode
There is a maximum number of result sets that a particular stored procedure can
return. The number of result sets returned is at most the number of REF CURSOR OUT
arguments for the stored procedure. It can return fewer result sets, but it can never
return more.
For the system described in Section 3.4.1.2, there is no maximum number of result sets
that can be returned. In the case of Model 1 (in Section 3.4.1.1), the maximum number
of result sets that a procedure can return is known, and that the driver can return to
Heterogeneous Services, is specified in the stored procedure by the number of REF
3-10 Oracle Database Heterogeneous Connectivity User's Guide
Data Dictionary Translations
CURSOR OUT arguments. If, when the stored procedure is executed, fewer result sets
than the maximum are returned, then the other REF CURSOR OUT arguments are set
to NULL.
Another problem for Model 2 database servers is that result sets must be retrieved in
the order in which they were placed on the wire by the database. This prevents
Heterogeneous Services from running in cursor mode when connecting to these
databases. To access result sets returned by these stored procedures, Heterogeneous
Services must be in sequential mode.
In sequential mode, the procedure description returned by the driver contains the
following:
■
All the input arguments of the remote stored procedure
■
None of the output arguments
■
One OUT argument of type REF CURSOR (corresponding to the first result set
returned by the stored procedure)
The client fetches from this REF CURSOR and then calls the virtual package function
DBMS_HS_RESULT_SET.GET_NEXT_RESULT_SET to fetch the REF CURSOR
corresponding to the next result set. This function call repeats until all result sets are
retrieved. The last result set returned will be the OUT arguments of the remote stored
procedure.
The primary limitations of sequential mode are:
■
■
Result sets returned by a remote stored procedure must be retrieved in the order
in which they were placed on the wire.
When a stored procedure is executed, all result sets returned by a previously
executed stored procedure are closed (regardless of whether or not the data was
retrieved).
See Also: Your gateway-specific manual for more information
about how result sets are supported through the gateway
3.5 Data Dictionary Translations
Most database systems have some form of data dictionary. A data dictionary is a
collection of information about the database objects that were created by various users
of the system. For a relational database, a data dictionary is a set of tables and views
that contain information about the data in the database. This information includes
information about the users who are using the system and about the objects that they
created (such as tables, views, and triggers). Almost all data dictionaries (regardless of
the database system) contain the same information, but each database system
organizes the information differently.
For example, the ALL_CATALOG Oracle data dictionary view gives a list of tables,
views, and sequences in the database. It has three columns: the first is called OWNER,
and it is the name of the owner of the object; the second is called TABLE_NAME, and it
is the name of the object; and the third is called TABLE_TYPE, and it is the data type.
This field has value TABLE, VIEW, SEQUENCE and so forth depending on the object
type. However, in Sybase, the same information is stored in two tables called
sysusers and sysobjects whose column names are different from those of the
Oracle ALL_CATALOG table. Additionally, in Oracle Database, the table type is a string
with a value such as TABLE or VIEW. With Sybase, it is a letter, for example, U means
user table; S means system table; V means view, and so forth.
Features of Oracle Database Gateways 3-11
Date-Time Data Types
If the client program requires information from the table ALL_CATALOG on a Sybase
system, it sends a query referencing ALL_CATALOG@database_link to a gateway.
Heterogeneous Services translates this query to an appropriate query on systables
and then sends the translated query to the Sybase system, for example:
SELECT SU.&quot;name&quot; OWNER, SO.&quot;name&quot; TABLE_NAME,
DECODE(SO.&quot;type&quot;, 'U ','TABLE', 'S ', 'TABLE', 'V ', 'VIEW')
TABLE_TYPE
FROM &quot;dbo&quot;.&quot;sysusers&quot;@remote_db SU, &quot;dbo&quot;.&quot;sysobjects&quot;@remote_db SO
WHERE SU.&quot;uid&quot; = SO.&quot;uid&quot; AND
(SO.&quot;type&quot; = 'V' OR SO.&quot;type&quot; = 'S' OR SO.&quot;type&quot; = 'U');
To relay the translation of a query on an Oracle data dictionary table to the equivalent
one on the non-Oracle system data dictionary table, Heterogeneous Services needs
data dictionary translations for that non-Oracle system. A data dictionary translation
is a view definition (essentially a SELECT statement) of one or more non-Oracle
system data dictionary tables that look like the Oracle data dictionary table, with the
same column names and the same formatting. Most data dictionary translations are
not as simple as the preceding example. Often, the information is scattered over many
tables, and the data dictionary translation is a complex join of those tables.
In some cases, an Oracle data dictionary table does not have a translation because the
information does not exist on the non-Oracle system. In such cases, the gateway must
not upload a translation, or the gateway might implement an alternative approach
called mimicking. If the gateway mimics a data dictionary table, it informs
Heterogeneous Services, and Heterogeneous Services will get the description of the
data dictionary table by querying the local database. When asked to retrieve data, it
will report that no rows were selected.
3.6 Date-Time Data Types
Oracle Database has five date-time data types:
■
TIMESTAMP
■
TIMESTAMP WITH TIME ZONE
■
TIMESTAMP WITH LOCAL TIME ZONE
■
INTERVAL YEAR TO MONTH
■
INTERVAL DAY TO SECOND
Heterogeneous Services generic code supports Oracle date-time data types in SQL and
stored procedures. Heterogeneous Services does not support these data types in data
dictionary translations or queries involving data dictionary translations.
Even though Heterogeneous Services generic code supports date-time data types,
support for a particular gateway depends on whether or not the driver for that
non-Oracle system implemented date-time support. Support, even when the driver
implements it, may be partial because of the limitations of the non-Oracle system. For
more information, see your gateway-specific documentation.
You must set the timestamp formats of the non-Oracle system in the gateway
initialization file. The parameters to set are HS_NLS_TIMESTAMP_FORMAT and HS_
NLS_TIMESTAMP_TZ_FORMAT. You should also set the local time zone for the
non-Oracle system in the initialization file by setting HS_TIME_ZONE.
See Also: Oracle Database SQL Language Reference for information
about datetime data types
3-12 Oracle Database Heterogeneous Connectivity User's Guide
Constraints on SQL in a Distributed Environment
3.7 Two-Phase Commit Protocol
Heterogeneous Services provides the infrastructure to implement the two-phase
commit protocol. The extent to which this is supported depends on the gateway and
the remote system. For more information, see your gateway-specific documentation.
See Also: Oracle Database Administrator's Guide for more
information about the two-phase commit protocol
3.8 Piecewise LONG Data Type
Earlier versions of gateways had limited support for the LONG data type. LONG is an
Oracle data type that can store up to 2 GB of character data or raw data (LONG RAW).
These earlier versions restricted the amount of LONG data to 4 MB because they treated
LONG data as a single piece. This caused memory and network bandwidth restrictions
on the size of the data that could be handled. Current gateways extended the
functionality to support the full 2 GB of heterogeneous LONG data. The gateways now
manage the data piecewise between the agent and Oracle Database, eliminating the
large memory and network bandwidth requirements.
The HS_LONG_PIECE_TRANSFER_SIZE Heterogeneous Services initialization
parameter can be used to set the size of the transferred pieces. For example, consider
retrieving 2 GB of LONG data from a heterogeneous source. A smaller piece requires
less memory, but it requires more round-trips to retrieve all the data. A larger piece
requires fewer round-trips, but it requires a larger amount of memory to store the
intermediate pieces internally. The initialization parameter can be used to tune a
system for the best performance, that is, for the best trade-off between round-trips and
memory requirements. If the initialization parameter is not set, the system uses 64 KB
as the default piece size.
Do not confuse this feature with piecemeal operations on
LONG data on the client side. Piecemeal fetch and insert operations
on the client side worked with the earlier versions of the gateways,
and they continue to do so. The only difference on the client side is
that, where earlier versions of the gateways were able to fetch a
maximum of 4 MB of LONG data, now they can retrieve the 2 GB of
LONG data. This is a significant improvement because 4 MB is only
0.2 percent of the data type's capacity.
Note:
3.9 SQL*Plus DESCRIBE Command
You can describe non-Oracle system objects using the SQL*Plus DESCRIBE command.
However, there are some limitations. For example, using heterogeneous links, you
cannot describe packages, sequences, synonyms, or types.
3.10 Constraints on SQL in a Distributed Environment
This section explains some of the constraints on SQL in a distributed environment.
These constraints apply to distributed environments that access non-Oracle systems or
remote Oracle databases.
This section contains the following topics:
■
Remote and Heterogeneous References
■
Important Restrictions
Features of Oracle Database Gateways 3-13
Constraints on SQL in a Distributed Environment
3.10.1 Remote and Heterogeneous References
Note: Many of the rules for heterogeneous access also apply to
remote references. For more information, see the distributed
database section of the Oracle Database Administrator's Guide.
A statement can, with restrictions, be executed on any database node referenced in the
statement or the local node. If all objects referenced are resolved to a single, referenced
node, Oracle attempts to execute a query at that node. You can force execution at a
referenced node by using the /*+ REMOTE_MAPPED */ or /*+ DRIVING_SITE */
hints. If a statement is forwarded to a node other than the node from where the
statement was issued, the statement is said to be remote-mapped.
There is complete data type checking support for remote-mapped statements. The
result provides consistent data type checking and complete data type coercion.
See Also: Section 4.5, &quot;Oracle Database Server SQL Construct
Processing&quot;
The ways in which statements can be remote-mapped are subject to specific rules or
restrictions. If these rules are not followed, an error occurs. As long as the statements
issued are consistent with all these rules, the order in which the rules are applied does
not matter. See Section 3.10.2 for these rules or restrictions.
Different constraints exist when you are using SQL for remote mapping in a
distributed environment. This distributed environment can include remote Oracle
databases as well as non-Oracle databases that are accessed through Oracle Database
gateways.
3.10.2 Important Restrictions
The following section lists some of the different rules or restrictions that exist when
you are using SQL for remote mapping in a distributed environment.
Note: In the examples that follow, remote_db refers to a remote
non-Oracle system while remote_oracle_db refers to a remote
Oracle Database.
Rule A: A data definition language statement cannot be remote-mapped.
In Oracle data definition language, the target object syntactically has no place for a
remote reference. Data definition language statements that contain remote references
are always executed locally. For Heterogeneous Services, this means it cannot directly
create database objects in a non-Oracle database using SQL.
However, there is an indirect way using passthrough SQL as shown in the following
example:
DECLARE
num_rows INTEGER;
BEGIN
num_rows := DBMS_HS_PASSTHROUGH.EXECUTE_IMMEDIATE@remote_db
(
'create table x1 (c1 char, c2 int)'
);
END;
3-14 Oracle Database Heterogeneous Connectivity User's Guide
Constraints on SQL in a Distributed Environment
Rule B: INSERT, UPDATE and DELETE statements with a remote target
table must be remote-mapped.
This rule is more restrictive for non-Oracle remote databases than for a remote Oracle
database. This is because the remote system cannot fetch data from the originating
Oracle database while executing data manipulation language (DML) statements
targeting tables in a non-Oracle system.
For example, to insert all local employees from the local emp table to a remote
non-Oracle emp table, use the following statement:
INSERT INTO emp@remote_db SELECT * FROM emp;
This statement is remote-mapped to the remote database. The remote-mapped
statement sent to the remote database contains a remote reference back to the
originating database for emp. Such a remote link received by the remote database is
called a callback link.
Even though callback links are supported in generic
Heterogeneous Services, they may not be implemented in all
Heterogeneous Services agents. Refer to your database gateway
documentation to determine if callback links work with the
database gateway that you are using.
Note:
If callback links are not supported by a particular gateway, the previous INSERT
statements returns the following error:
ORA-02025: all tables in the SQL statement must be at the remote database
The workaround is to write a PL/SQL block. For example:
DECLARE
CURSOR remote_insert IS SELECT * FROM emp;
BEGIN
FOR rec IN remote_insert LOOP
INSERT INTO emp@remote_db (empno, ename, deptno) VALUES (
rec.empno,
rec.ename,
rec.deptno
);
END loop;
END;
Another special case involves session-specific SQL functions such as USER, USERENV,
and SYSDATE. These functions need to be executed at the originating site. A
remote-mapped statement containing these functions contains a callback link. For a
non-Oracle database for which callbacks are not supported, this can (by default) result
in a restriction error.
For example, consider the following statement:
DELETE FROM emp@remote_db WHERE hiredate &gt; sysdate;
The previous statement returns the following error message:
ORA-02070: database REMOTE_DB does not support special functions in this context
This can be resolved by replacing special functions with a bind variable. For example:
DELETE FROM emp@remote_db WHERE hiredate &gt; :1;
Features of Oracle Database Gateways 3-15
Constraints on SQL in a Distributed Environment
Rule C: Object features like tables with nested table columns, ADT
columns, Opaque columns, or Ref Columns cannot be remote-mapped.
Currently, these column types are not supported for heterogeneous access. Hence, this
limitation is not directly encountered.
Rule D: SQL statements containing operators and constructs that are not
supported at the remote site cannot be remote-mapped.
In the case of an INSERT, UPDATE, or DELETE, this means that the SQL statement
cannot be executed (see Rule B). However, you might still be able to execute the SQL
statement if the unsupported operator or construct can be executed through a callback
link.
In the case of a SELECT, you can always execute a statement affected by this rule as
long as none of the remaining rules require the statement to be remote mapped. The
SELECT statements affected by this rule are executed by fetching all the necessary data
through a remote SELECT operation, and processing the unsupported operator or
construct locally using the local SQL engine.
A remote SELECT operation is the operation that retrieves rows from the remote table
as opposed to an operation that retrieves data from the local table. In the worse
possible case of a remote SELECT, Oracle does a full table scan. A full table scan is a
fetch of all the data in the remote table across the network without any filtering (for
example, SELECT * FROM EMP).
Full table scans are expensive and, therefore, Oracle attempts to avoid them. If there
are indexes on the remote table that can be used, these indexes are used in a WHERE
clause predicate to reduce the number of rows fetched across the network.
You can check the SQL statement generated by Oracle Database by explaining the
statement and querying the OTHER column of the explain plan table for each REMOTE
operation.
See Also: Section 3.11.1 for more information on how to interpret
explain plans with remote references
For example, consider the following statement:
SELECT COUNT(*) FROM emp@remote_db WHERE hiredate &lt; sysdate;
The statement returns the following output:
COUNT(*)
---------14
1 row selected.
The remote table scan is:
SELECT hiredate FROM emp;
The predicate converted to a filter cannot be generated back and passed down to the
remote operation because sysdate is not supported by the remote_db or evaluation
rules. Thus sysdate must be executed locally.
Because the remote table scan operation is only partially
related to the original query, the number of rows retrieved can be
significantly larger than expected and can have a significant impact
on performance.
Note:
3-16 Oracle Database Heterogeneous Connectivity User's Guide
Oracle's Optimizer and Heterogeneous Services
Rule E: SQL statement containing a table expression cannot be
remote-mapped.
This limitation is not directly encountered because table expressions are not supported
in the heterogeneous access module.
Rule F: If a SQL statement selects LONG data, the statement must be
mapped to the node where the table containing the LONG data resides.
Consider the following type of statement:
SELECT long1 FROM table_with_long@remote_db, dual;
The previous statement returns the following error message (if callback links are not
supported):
ORA-02025: all tables in the SQL statement must be at the remote database
Rule G: The statement must be mapped to the node on which the table or
tables with columns referenced in the FOR UPDATE OF clause resides
when the SQL statement is of form &quot;SELECT...FOR UPDATE OF...&quot;
When the SQL statement is of the form SELECT...FOR UPDATE OF..., the
statement must be mapped to the node on which the table or tables with columns
referenced in the FOR UPDATE OF clause resides.
For example, consider the following statement:
SELECT ename FROM emp@remote_db WHERE hiredate &lt; sysdate FOR UPDATE OF empno;
The previous statement returns the following error message if it cannot be
remote-mapped:
ORA-02070: database REMOTE_DB does not support special functions in this context
Rule H: If the SQL statement contains a SEQUENCE or sequences, then
the statement must be mapped to the site where each sequence resides.
This rule is not encountered for the heterogeneous access module because remote
non-Oracle sequences are not supported.
Rule I: If the statement contains a user-defined operator or operators, then
the statement must be mapped to the node where each operator is defined.
If the statement contains a user-defined operator, the entire statement needs to be
remote-mapped to the database node where the operator is defined.
Rule J: A statement containing duplicate bind variables cannot be
remote-mapped.
The workaround for this restriction is to use unique bind variables and bind by
number.
3.11 Oracle's Optimizer and Heterogeneous Services
Oracle's optimizer can be used with Heterogeneous Services. Heterogeneous Services
collects certain table and index statistics information on the respective non-Oracle
system tables and passes this information back to Oracle Database. The Oracle
cost-based optimizer uses this information when building the query plan.
Features of Oracle Database Gateways 3-17
Oracle's Optimizer and Heterogeneous Services
There are several other optimizations that the cost-based optimizer performs. The
most important ones are remote sort elimination and remote joins.
This section contains the following topics:
■
Example: Using Index and Table Statistics
■
Example: Remote Join Optimization
■
Optimizer Restrictions for Non-Oracle Access
3.11.1 Example: Using Index and Table Statistics
Consider the following statement where you create a table in the Oracle database with
10 rows:
CREATE TABLE T1 (C1 number);
Analyze the table using the DBMS_STATS package. For example:
DBMS_STATS.GATHER_TABLE_STATS (’SCOTT’,’T1’);
DBMS_STATS.GENERATE_STATS (’SCOTT’,’T1’);
The preceding example assumes the schema name is SCOTT and the table name is T1.
See the Oracle Database PL/SQL Packages and Types Reference for more information about
the DBMS_STATS package.
Create a table in the non-Oracle system with 1000 rows.
Issue the following SQL statement:
SELECT a.* FROM remote_t1@remote_db a, T1 b
WHERE a.C1 = b.C1;
The Oracle optimizer issues the following SQL statement to the agent:
SELECT C1 FROM remote_t1@remote_db;
This fetches all 1000 rows from the non-Oracle system and performs the join in the
Oracle database.
If we add a unique index on the column C1 in the table remote_t1, and issue the
same SQL statement again, the agent receives the following SQL statement for each
value of C1 in the local t1:
...
SELECT C1 FROM remote_t1@remote_db WHERE C1 = ?;
...
? is the bind parameter marker. Also, join predicates
containing bind variables generated by Oracle are generated only
for nested loop join methods.
Note:
To verify the SQL execution plan, generate an explain plan for the SQL statement.
First, load utlxplan in the admin directory.
Enter the following:
EXPLAIN PLAN FOR SELECT a.* FROM remote_t1@remote_db a, T1 b
WHERE a.C1 = b.C1;
Execute the utlxpls utility script by entering the following statement.
3-18 Oracle Database Heterogeneous Connectivity User's Guide
Oracle's Optimizer and Heterogeneous Services
@utlxpls
OPERATION REMOTE indicates that remote SQL is being referenced.
To find out what statement is sent, enter the following statement:
SELECT ID, OTHER FROM PLAN_TABLE WHERE OPERATION = 'REMOTE';
3.11.2 Example: Remote Join Optimization
The following is an example of the remote join optimization capability of the Oracle
database.
The explain plan that uses tables from a non-Oracle system
can differ from similar statements with local or remote Oracle table
scans. This is because of the limitation on the statistics available to
Oracle for non-Oracle tables. Most importantly, column selectivity
is not available for non-unique indexes of non-Oracle tables.
Because of the limitation of the statistics available, the following
example is not necessarily what you encounter when doing remote
joins and is intended for illustration only.
Note:
Consider the following example:
EXPLAIN PLAN FOR
SELECT e.ename, d.dname, f.ename, f.deptno FROM
dept d,
emp@remote_db e,
emp@remote_db f
WHERE e.mgr = f.empno
AND e.deptno = d.deptno
AND e.empno = f.empno;
@utlxpls
You should see output similar to the following:
PLAN_TABLE_OUTPUT
---------------------------------------------------------------------------------------------------------------------------------------------------------| Id
| Operation
| Name | Rows | Bytes | Cost
| Inst |IN-OUT|
--------------------------------------------------------------------------|
0
| SELECT STATEMENT
|
| 2000
|
197K|
205 |
|* 1
| HASH JOIN
|
| 2000
|
197K|
205 |
|
2
| TABLE ACCESS FULL | DEPT
| 21
|
462 |
2 |
|* 3
| HASH JOIN
|
| 2000
|
154K|
201 |
|
4
| REMOTE
|
| 2000
| 66000
|
52 |
|
5
| REMOTE
|
| 2000
| 92000
|
52 |
--------------------------------------------------------------------------PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Features of Oracle Database Gateways 3-19
Oracle's Optimizer and Heterogeneous Services
Query Block Name / Hint Alias (identified by operation id):
----------------------------------------------------------1
2
3
4
5
-
sel$1
sel$1
sel$1
sel$1
sel$1
/
/
/
/
/
D
D
F
F
E
Predicate Information (identified by operation id):
PLAN_TABLE_OUTPUT
---------------------------------------------------------------------------------------------------------------------------------1 - access(&quot;E&quot;.&quot;DEPTNO&quot;=&quot;D&quot;.&quot;DEPTNO&quot;)
3 - access(&quot;E&quot;.&quot;MGR&quot;=&quot;F&quot;.&quot;EMPNO&quot; AND &quot;E&quot;.&quot;EMPNO&quot;=&quot;F&quot;.&quot;EMPNO&quot;)
Issue the following statement:
SET long 300
SELECT other FROM plan_table WHERE operation = 'REMOTE';
You should see output similar to the following:
OTHER
-------------------------------------------------------------------------------SELECT
SELECT
SELECT
SELECT
&quot;EMPNO&quot;,&quot;ENAME&quot;,&quot;DEPTNO&quot; FROM &quot;EMP&quot;
&quot;EMPNO&quot;,&quot;ENAME&quot;,&quot;MGR&quot;,&quot;DEPTNO&quot; FROM &quot;EMP&quot;
&quot;EMPNO&quot;,&quot;ENAME&quot;,&quot;DEPTNO&quot; FROM &quot;EMP&quot;
&quot;EMPNO&quot;,&quot;ENAME&quot;,&quot;MGR&quot;,&quot;DEPTNO&quot; FROM &quot;EMP&quot;
3.11.3 Optimizer Restrictions for Non-Oracle Access
The following are optimizer restrictions for non-Oracle system access:
■
■
There are no column statistics for remote objects. This can result in poor execution
plans. Verify the execution plan and use hints to improve the plan.
There is no optimizer hint to force a remote join. However, there is a remote query
block optimization that can be used to rewrite the query slightly in order to get a
remote join.
The example from the previous section can be rewritten to the following form:
SELECT v.ename, d.dname, d.deptno FROM dept d,
(SELECT /*+ NO_MERGE */
e.deptno deptno, e.ename ename emp@remote_db e, emp@remote_db f
WHERE e.mgr = f.empno
AND e.empno = f.empno;
)
WHERE v.deptno = d.deptno;
This example guarantees a remote join because it has been isolated in a nested query
with the NO_MERGE hint.
3-20 Oracle Database Heterogeneous Connectivity User's Guide
4
Using Heterogeneous Services Agents
This chapter explains how to use Heterogeneous Services (HS) agents. For installing
and configuring the agents, refer to the Oracle Database gateway installation and
configuration guides. This chapter contains the following sections:
■
Initialization Parameters
■
Optimizing Data Transfers Using Bulk Fetch
■
Optimizing Data Loads Using Parallel Load
■
Registering Agents
■
Oracle Database Server SQL Construct Processing
■
Executing User-Defined Functions on a Non-Oracle Database
■
Using Synonyms
■
■
Copying Data from the Oracle Database Server to the Non-Oracle Database
System
Copying Data from the Non-Oracle Database System to the Oracle Database
Server
■
Using Heterogeneous Services Data Dictionary Views
■
Using the Heterogeneous Services Dynamic Performance Views
4.1 Initialization Parameters
Configure the gateway using initialization parameters. This is done by creating an
initialization file and setting the desired parameters in this file. See Section 2.5 for
configuration information.
Heterogeneous Services initialization parameters are distinct from Oracle Database
initialization parameters. Heterogeneous Services initialization parameters are set in
the Heterogeneous Services initialization file and not in the Oracle database
initialization parameter file (init.ora file). There is a Heterogeneous Services
initialization file for each gateway instance.
The following sections describe:
■
Encrypting Initialization Parameters
■
Gateway Initialization Parameters
Using Heterogeneous Services Agents
4-1
Initialization Parameters
4.1.1 Encrypting Initialization Parameters
Initialization parameters may contain sensitive information, such as user IDs or
passwords. Initialization parameters are stored in plain text files and are insecure. An
encryption feature has been added to Heterogeneous Services making it possible to
encrypt parameter values. This is done through the dg4pwd utility. To use this feature
requires setting the value of a parameter in the initialization file to an unquoted
asterisk (*). For example:
HD_FDS_CONNECT_INFO = *
With the value set to this security marker, all Heterogeneous Services agents know that
the real value will be stored in a related, encrypted password file. The name of this file
will be initsid.pwd, where sid is the Oracle system identifier used for the gateway.
This file is created by the dg4pwd utility in the current directory containing the
initialization file. Running the utility prompts for the real value of the parameter,
which the utility will encrypt and store in the password file. It should be noted that
encrypted initialization parameters are implicitly treated as PRIVATE parameters and
are not uploaded to the server.
4.1.1.1 Using the dg4pwd Utility
The dg4pwd utility is used to encrypt initialization parameters that would normally be
stored in the initialization parameter file in plain text. The utility works by reading the
initialization parameter file in the current directory and looking for parameters having
a security marker for the value. The security marker is an unquoted asterisk (*). This
designates that the value of this parameter is to be stored in an encrypted form in a
password file. The following is an example of an initialization parameter set to this
value:
HS_FDS_CONNECT_INFO = *
The initialization parameter file in the current directory is first edited to set the value
of the parameter to this security marker. Then the utility is run, specifying the gateway
SID on the command line, with an optional user ID to designate a different owner of
the encrypted information. The utility reads the initialization parameter file and
prompts you to enter the real values that are to be encrypted.
The syntax of the command is:
dg4pwd [sid] {userid}
Where [sid] is the SID of the gateway and {userid} is an optional user ID used to
encrypt the contents. If no user ID is specified, then the current user's ID is used.
Values are encrypted using this ID. In order to decrypt the values, the agent must be
run as that user.
The following example assumes a gateway SID of SYBASE:
dg4pwd SYBASE
ORACLE Gateway Password Utility
Constructing password file for Gateway SID SYBASE
Enter the value for HS_FDS_CONNECT_INFO
sybasew
In the previous example, the initialization parameter file, initSYBASE.ora, is read.
The parameter, HS_FDS_CONNECT_INFO, is identified as requiring encryption. Enter
the value (for example, sybasew) and presses enter. If more parameters require
encryption, they are prompted for in turn. The encrypted data is stored in the same
directory as the initialization file.
4-2 Oracle Database Heterogeneous Connectivity User's Guide
Optimizing Data Transfers Using Bulk Fetch
Any initialization parameters needing encryption should be encrypted before using
the Oracle Database gateway.
4.1.2 Gateway Initialization Parameters
Gateway initialization parameters can be divided into two groups. One is a set of
generic initialization parameters that are common to all gateways and the other is a set
of initialization parameters that are specific to individual gateways. The following
generic initialization parameters are the only initialization parameters discussed in
this document:
HS_BULK
HS_CALL_NAME
HS_COMMIT_POINT_STRENGTH
HS_DB_DOMAIN
HS_DB_INTERNAL_NAME
HS_DB_NAME
HS_DESCRIBE_CACHE_HWM
HS_FDS_CONNECT_INFO
HS_FDS_DEFAULT_SCHEMA_NAME
HS_FDS_SHAREABLE_NAME
HS_FDS_TRACE_LEVEL
HS_LANGUAGE
HS_LONG_PIECE_TRANSFER_SIZE
HS_NLS_DATE_FORMAT
HS_NLS_DATE_LANGUAGE
HS_NLS_NCHAR
HS_NLS_NUMERIC_CHARACTERS
HS_NLS_TIMESTAMP_FORMAT
HS_NLS_TIMESTAMP_TZ_FORMAT
HS_OPEN_CURSORS
HS_ROWID_CACHE_SIZE
HS_RPC_FETCH_REBLOCKING
HS_RPC_FETCH_SIZE
HS_TIME_ZONE
Do not use the PRIVATE keyword when setting any of these parameters. Using the
PRIVATE keyword prevents the parameter from being uploaded to the server and can
cause errors in SQL processing. None of these parameters needs to be set in the
environment, so you do not need to use the SET keyword.
See Also: Individual gateway documentation for the list of
initialization parameters specific to a gateway
4.2 Optimizing Data Transfers Using Bulk Fetch
When an application fetches data from a non-Oracle system using Heterogeneous
Services, data is transferred:
1.
From the non-Oracle system to the agent process.
2.
From the agent process to Oracle Database.
3.
From Oracle Database to the application.
Oracle optimizes all three data transfers, as illustrated in Figure 4–1.
Using Heterogeneous Services Agents
4-3
Optimizing Data Transfers Using Bulk Fetch
Figure 4–1 Optimizing Data Transfers
Client
Non-Oracle System
Agent
Oracle Server
Array fetch
with OCI/Pro*
or other tool
HS_RPC_FETCH_SIZE
HS_FDS_FETCH_ROWS
This section contains the following topics:
■
Using OCI, an Oracle Precompiler, or Another Tool for Array Fetches
■
Controlling the Array Fetch Between Oracle Database and the Agent
■
Controlling the Array Fetch Between the Agent and the Non-Oracle System
■
Controlling the Reblocking of Array Fetches
4.2.1 Using OCI, an Oracle Precompiler, or Another Tool for Array Fetches
You can optimize data transfers between your application and Oracle Database by
using array fetches. See your application development tool documentation for
information about array fetching and how to specify the amount of data to be sent and
each network round-trip.
4.2.2 Controlling the Array Fetch Between Oracle Database and the Agent
When Oracle retrieves data from a non-Oracle system, the Heterogeneous Services
initialization parameter, HS_RPC_FETCH_SIZE, defines the number of bytes sent for
each fetch between the agent and Oracle Database. The agent fetches data from the
non-Oracle system until one of the following occurs:
■
It has accumulated the specified number of bytes to send back to Oracle Database.
■
The last row of the result set is fetched from the non-Oracle system.
4.2.3 Controlling the Array Fetch Between the Agent and the Non-Oracle System
The initialization parameter, HS_FDS_FETCH_ROWS, determines the number of rows
to be retrieved from a non-Oracle system. Note that the array fetch must be supported
4-4 Oracle Database Heterogeneous Connectivity User's Guide
Registering Agents
by the agent. See your agent-specific documentation to ensure that your agent
supports array fetching.
4.2.4 Controlling the Reblocking of Array Fetches
By default, an agent fetches data from the non-Oracle system until it has enough data
retrieved to send back to the system. It continues until the number of bytes fetched
from the non-Oracle system is equal to or higher than the value of HS_RPC_FETCH_
SIZE initialization parameter. In other words, the agent reblocks the data between the
agent and Oracle Database in sizes defined by the value of the HS_RPC_FETCH_SIZE
initialization parameter.
When the non-Oracle system supports array fetches, you can immediately send the
data fetched from the non-Oracle system by the array fetch to Oracle Database without
waiting until the exact value of the HS_RPC_FETCH_SIZE initialization parameter is
reached. That is, you can stream the data from the non-Oracle system to Oracle
Database and disable reblocking by setting the value of the HS_RPC_FETCH_
REBLOCKING initialization parameter to OFF.
For example, assume that you set HS_RPC_FETCH_SIZE to 64 kilobytes (KB) and HS_
FDS_FETCH_ROWS to 100 rows. Also assume that each row is approximately 600 bytes
in size, so that the 100 rows are approximately 60 KB. When the HS_RPC_FETCH_
REBLOCKING initialization parameter is set to ON, the agent starts fetching 100 rows
from the non-Oracle system.
Because there is only 60 KB of data in the agent, the agent does not send the data back
to Oracle Database. Instead, the agent fetches the next 100 rows from the non-Oracle
system. Because there is now 120 KB of data in the agent, the first 64 KB can be sent
back to Oracle Database.
Now there is 56 KB of data left in the agent. The agent fetches another 100 rows from
the non-Oracle system before sending the next 64 KB of data to Oracle Database. By
setting the HS_RPC_FETCH_REBLOCKING initialization parameter to OFF, the first 100
rows are immediately sent back to the Oracle database server.
4.3 Optimizing Data Loads Using Parallel Load
The DBMS_HS_PARALLEL PL/SQL package enables parallel processing for
heterogeneous targets access. This package improves performance when retrieving
data from a large foreign table.
DBMS_HS_PARALLEL is compiled with an authorization ID of CURRENT_USER,
meaning it uses invoker’s rights. In other words, all procedures in this package are
executed with the privileges of the calling user.
For additional information about the procedures, see Oracle Database PL/SQL Packages
and Types Reference.
4.4 Registering Agents
Registration is an operation through which Oracle stores information about an agent
in the data dictionary. Agents do not have to be registered. If an agent is not registered,
Oracle stores information about the agent in memory instead of in the data dictionary.
When a session involving an agent terminates, this information ceases to be available.
Self-registration is an operation in which a database administrator sets an
initialization parameter that lets the agent automatically upload information into the
Using Heterogeneous Services Agents
4-5
Registering Agents
data dictionary. Self-registration occurs when the HS_AUTOREGISTER initialization
parameter is set to TRUE (default).
Note: HS_AUTOREGISTER is an Oracle initialization parameter
that you set in the init.ora file; it is not a Heterogeneous Services
initialization parameter that is set in the gateway initialization file.
This section contains the following topics:
■
Enabling Agent Self-Registration
■
Disabling Agent Self-Registration
4.4.1 Enabling Agent Self-Registration
To ensure correct operation over heterogeneous database links, agent self-registration
automates updates to Heterogeneous Services configuration data that describe agents
on remote hosts. Agent self-registration is the default behavior. If you do not want to
use the agent self-registration feature, set the HS_AUTOREGISTER initialization
parameter to FALSE.
Both the server and the agent rely on three types of information to configure and
control operation of the Heterogeneous Services connection. These three sets of
information are collectively called HS configuration data:
Heterogeneous
Services Configuration
Data
Description
Heterogeneous Services
initialization parameters
Provide control over various connection-specific details of
operation.
Capability definitions
Identify details like SQL language features supported by the
non-Oracle data source.
Data dictionary
translations
Map references to Oracle data dictionary tables and views into
equivalents specific to the non-Oracle data source.
See Also:
Section 4.4.1.3, &quot;Specifying HS_AUTOREGISTER&quot;
4.4.1.1 Using Agent Self-Registration to Avoid Configuration Mismatches
HS configuration data is stored in the data dictionary of the Oracle database server.
Because the agent may be remote and may therefore be administered separately,
several circumstances can lead to configuration mismatches between servers and
agents. For example:
■
■
■
■
An agent can be newly installed on a separate computer so that the server has no
Heterogeneous Services data dictionary content to represent the agent's
Heterogeneous Services configuration data.
A server can be newly installed and lack the necessary Heterogeneous Services
configuration data for existing agents and non-Oracle data stores.
A non-Oracle instance can be upgraded from an older version to a newer version,
requiring modification of the Heterogeneous Services configuration data.
A Heterogeneous Services agent at a remote site can be upgraded to a new version
or patched, requiring modification of the Heterogeneous Services configuration
data.
4-6 Oracle Database Heterogeneous Connectivity User's Guide
Registering Agents
■
A database administrator (DBA) at the non-Oracle site can change the agent setup,
possibly for tuning or testing purposes, in a manner which affects Heterogeneous
Services configuration data.
Agent self-registration permits successful operation of Heterogeneous Services in all
these scenarios. Specifically, agent self-registration enhances interoperability between
any Oracle database server and any Heterogeneous Services agent (if each is Version
8.0.3 or higher). The basic mechanism for this functionality is the ability to upload
Heterogeneous Services configuration data from agents to servers.
Self-registration provides automatic updating of Heterogeneous Services configuration
data residing in the Oracle database server data dictionary. This update ensures that
the agent self-registration uploads need to be done only once, on the initial use of a
previously unregistered agent. Instance information is uploaded on each connection,
not stored in the server data dictionary.
4.4.1.2 Understanding Agent Self-Registration
The Heterogeneous Services agent self-registration feature can perform the following
tasks:
■
■
■
Identify the agent and the non-Oracle data store to the Oracle database server
Permit agents to define Heterogeneous Services initialization parameters for use
both by the agent and connected Oracle servers
Upload capability definitions and data dictionary translations, if available, from a
Heterogeneous Services agent during connection initialization
The upload of class information occurs only when the class
is undefined in the server data dictionary. Similarly, instance
information is uploaded only if the instance is undefined in the
server data dictionary.
Note:
The information required for agent self-registration is accessed in the server data
dictionary by using these agent-supplied names:
■
FDS_CLASS
■
FDS_CLASS_VERSION
See Also: Section 4.10, &quot;Using Heterogeneous Services Data
Dictionary Views&quot; to learn how to use the Heterogeneous Services
data dictionary views
4.4.1.2.1 FDS_CLASS and FDS_CLASS_VERSION FDS_CLASS and FDS_CLASS_VERSION
are defined by Oracle or by third-party vendors for each individual Heterogeneous
Services agent and version. Oracle Heterogeneous Services concatenates these names
to form FDS_CLASS_NAME, which is used as a primary key to access class information
in the server data dictionary.
FDS_CLASS should specify the type of non-Oracle data store to be accessed and FDS_
CLASS_VERSION should specify a version number for both the non-Oracle data store
and the agent that connects to it. Note that when any component of an agent changes,
FDS_CLASS_VERSION must also change to uniquely identify the new release.
Using Heterogeneous Services Agents
4-7
Registering Agents
This information is uploaded when you initialize each
connection.
Note:
4.4.1.2.2 FDS_INST_NAME Instance-Specific Information can be stored in the server
data dictionary. The instance name, FDS_INST_NAME, is configured by the database
administrator (DBA) who administers the agent. How the DBA performs this
configuration depends on the specific agent in use.
The Oracle database server uses FDS_INST_NAME to look up instance-specific
configuration information in its data dictionary. Oracle uses the value as a primary key
for columns of the same name in these views:
■
FDS_INST_INIT
■
FDS_INST_CAPS
■
FDS_INST_DD
Server data dictionary accesses that use FDS_INST_NAME also use FDS_CLASS_NAME
to uniquely identify configuration information rows. For example, if you port a
database from class Sybase816 to class Sybase817, both databases can simultaneously
operate with instance name SCOTT and use separate sets of configuration information.
Unlike class information, instance information is not automatically self-registered in
the server data dictionary:
■
■
If available, instance information is always uploaded by the agent. However, it is
never stored in the server data dictionary. Instead, the information is kept in
memory and it is only valid for that connection.
If the server data dictionary contains instance information, it represents the DBA's
defined setup details which correspond to the instance configuration. Data
dictionary defined instance information takes precedence over class information.
However, uploaded instance information takes precedence over data dictionary
defined instance information.
4.4.1.3 Specifying HS_AUTOREGISTER
The HS_AUTOREGISTER Oracle database server initialization parameter enables or
disables automatic self-registration of Heterogeneous Services agents. Note that this
parameter is specified in the Oracle initialization parameter file, not the agent
initialization file. For example, you can set the parameter as follows:
HS_AUTOREGISTER = TRUE
When set to TRUE, the agent uploads information describing a previously unknown
agent class or a new agent version into the server's data dictionary.
Oracle recommends that you use the default value for this parameter (TRUE), which
ensures that the server's data dictionary content always correctly represents definitions
of class capabilities and data dictionary translations as used in Heterogeneous Services
connections.
See Also:
Oracle Database Reference for a description of this
parameter
4.4.2 Disabling Agent Self-Registration
To disable agent self-registration, set the HS_AUTOREGISTER initialization parameter
as follows:
4-8 Oracle Database Heterogeneous Connectivity User's Guide
Oracle Database Server SQL Construct Processing
HS_AUTOREGISTER = FALSE
Disabling agent self-registration means that agent information is not stored in the data
dictionary. Consequently, the Heterogeneous Services data dictionary views are not
useful sources of information. Nevertheless, the Oracle server still requires
information about the class and instance of each agent. If agent self-registration is
disabled, the server stores this information in local memory.
4.5 Oracle Database Server SQL Construct Processing
Heterogeneous Services and the gateway rewrite SQL statements when the statements
need to be translated or postprocessed.
For the following examples, assume the INITCAP function is not supported in the
non-Oracle database. Consider a program that requests the following from the
non-Oracle database. For example:
SELECT &quot;COLUMN_A&quot; FROM &quot;test&quot;@remote_db
WHERE &quot;COLUMN_A&quot; = INITCAP(&quot;COLUMN_B&quot;);
The non-Oracle database does not recognize the INITCAP function, so the Oracle
database server fetches the data from the table test in the remote database and filters
the results locally. The gateway rewrites the SELECT statement as follows:
SELECT &quot;COLUMN_A&quot;, &quot;COLUMN_B&quot; FROM &quot;test&quot;@remote_db;
The results of the query are sent from the gateway to Oracle and are filtered by the
Oracle database server.
If a string literal or bind variable is supplied in place of &quot;COLUMN_B&quot; as shown in the
previous example, the Heterogeneous Services component of the Oracle server would
apply the INITCAP function before sending the SQL command to the gateway. For
example, if the following SQL command is issued:
SELECT &quot;COLUMN_A&quot; FROM &quot;test&quot;@remote_db WHERE &quot;COLUMN_A&quot; = INITCAP('jones');
The following SQL command would be sent to the gateway:
SELECT &quot;COLUMN_A&quot; FROM &quot;test&quot;@remote_db WHERE &quot;COLUMN_A&quot; = 'Jones';
Consider the following UPDATE request:
UPDATE &quot;test&quot;@remote_db SET &quot;COLUMN_A&quot; = 'new_value'
WHERE &quot;COLUMN_A&quot; = INITCAP(&quot;COLUMN_B&quot;);
In this case, the Oracle database server and the gateway cannot compensate for the
lack of support at the non-Oracle side, so an error is issued.
If a string literal or bind variable is supplied in place of &quot;COLUMN_B&quot; as shown in the
preceding example, the Heterogeneous Services component of the Oracle server would
apply the INITCAP function before sending the SQL command to the gateway. For
example, if the following SQL command is issued:
UPDATE &quot;test&quot;@remote_db SET &quot;COLUMN_A&quot; = 'new_value'
WHERE &quot;COLUMN_A&quot; = INITCAP('jones');
The following SQL command would be sent to the gateway:
UPDATE &quot;test&quot;@remote_db SET &quot;COLUMN_A&quot; = 'new_value'
WHERE &quot;COLUMN_A&quot; = 'Jones';
Using Heterogeneous Services Agents
4-9
Executing User-Defined Functions on a Non-Oracle Database
In previous releases, the preceding UPDATE statement would have raised an error due
to the lack of INITCAP function support in the non-Oracle database.
4.5.1 Data Type Checking Support for a Remote-Mapped Statement
The Oracle database has always performed data type checking and data type coercion
in a homogeneous environment. For example, SELECT * FROM EMP WHERE
EMPNO='7934' would return the same result as SELECT * FROM EMPNO WHERE
EMPNO=7934. There is also full data type checking support for remote-mapped
statements in a heterogeneous environment. In general, the operands in SQL
statements whether its a column, literal, or bind variable would be processed
internally for data type checking. Consider the following examples:
SELECT * FROM EMP@LINK WHERE NUMBER_COLUMN='123'
SELECT * FROM EMP@LINK WHERE NUMBER_COLUMN=CHAR_COLUMN;
SELECT * FROM EMP@LINK WHERE NUMBER_COLUMN=CHAR_BIND_VARIABLE;
Most non-Oracle databases do not support data type coercion, and the previous
statements fail if they are sent to a non-Oracle database as is. The Heterogeneous
Services component for the Oracle database performs data type checking and the
necessary data type coercion before sending an acceptable statement to a non-Oracle
database.
Data type checking provides consistent behavior on post-processed or remote-mapped
statements. Consider the following two statements:
SELECT * FROM EMP@LINK WHERE TO_CHAR(EMPNO)='7933' + '1';
And:
SELECT * FROM EMP@LINK WHERE EMPNO='7933' + '1';
Both of the previous statements provide the same result and coercion regardless if the
TO_CHAR function is supported in the non-Oracle database or not. Now, consider the
following statement:
SELECT * FROM EMP@LINK WHERE EMPNO='123abc' + '1';
As data type checking is enforced, the coercion attempt within Oracle generates an
error and returns it without sending any statements to a non-Oracle database.
In summary, there is consistent data type checking and coercion behavior regardless of
post-processed or remote-mapped statements.
4.6 Executing User-Defined Functions on a Non-Oracle Database
You can execute user-defined functions in a remote non-Oracle database. For example:
SELECT getdeptforemp@Remote_DB(7782) FROM dual;
In this example, a SELECT statement was issued that executes a user-defined function
in the remote database that returns department information for employee 7782.
When the remote function resides in an Oracle database, the Oracle database
automatically ensures that the remote function does not update any database state
(such as updating rows in a database or updating the PL/SQL package state). The
gateway cannot verify this when the remote function resides in a non-Oracle database.
Therefore, you are responsible for ensuring that the user-defined functions do not
update the state in any database. Ensuring no updates to the database is required to
guarantee read consistency.
4-10 Oracle Database Heterogeneous Connectivity User's Guide
Using Synonyms
As a security measure, you must specify the functions that you want to execute
remotely and their owners in the HS_CALL_NAME parameter in the gateway-specific
initialization parameter file. For example:
HS_CALL_NAME = &quot;owner1.A1, owner2.A2 &quot;
owner1 and owner2 are the remote function owner names. A1 and A2 are the remote
function names. You do not need to specify the remote function owner in the SQL
statement. By default, the remote function needs to reside in the schema that the
Database Gateway connects to. If this is not the case, then you must specify the owner
of the remote function in the SQL statement.
Some other examples of executing user-defined remote functions are as follows:
■
A remote function in a subquery
The function uses the employee_id column data to retrieve the department_id
from the EMPLOYEES table in the remote database. The outer query then
determines all department numbers in the remote database that match the
returned list.
SELECT * FROM departments@remotedb
WHERE department_id IN
(SELECT
getdeptforemp@remotedb (employee_id)
FROM employees@remotedb);
■
Applying a local function to the result of a user-defined remote function
This query returns the maximum salary of all employees on the remote database.
SELECT max (getsalforemp@remotedb (employee_id))
FROM employees@remotedb;
■
A DML statement
The statement uses the output from a user-defined query in the remote database to
update the salary column with new salary information.
UPDDATE employee_history
SET salary = emp_changed_salary@remote_db;
In these examples, the Oracle database passes the function name and owner to the
Database Gateway. The user-defined function is executed on the remote database.
4.7 Using Synonyms
You can provide complete data location transparency and network transparency by
using the synonym feature of the Oracle database server. When a synonym is defined,
you do not have to know the underlying table or network protocol. A synonym can be
public, which means that all Oracle users can refer to the synonym. A synonym can
also be defined as private, which means every Oracle user must have a synonym
defined to access the non-Oracle table.
The following statement creates a systemwide synonym for the emp table in the
schema of user ORACLE in the Sybase database:
CREATE PUBLIC SYNONYM emp FOR &quot;ORACLE&quot;.&quot;EMP&quot;@SYBS;
See Also: Oracle Database Administrator's Guide for information
about synonyms
Using Heterogeneous Services Agents 4-11
Copying Data from the Oracle Database Server to the Non-Oracle Database System
4.7.1 Example of a Distributed Query
Modify these examples for your environment. Do not try to
execute them as they are written.
Note:
The following statement joins data between the Oracle database server, an IBM DB2
database, and a Sybase database:
SELECT O.CUSTNAME, P.PROJNO, E.ENAME, SUM(E.RATE*P.&quot;HOURS&quot;)
FROM ORDERS@DB2 O, EMP@ORACLE9 E, &quot;PROJECTS&quot;@SYBS P
WHERE O.PROJNO = P.&quot;PROJNO&quot;
AND P.&quot;EMPNO&quot; = E.EMPNO
GROUP BY O.CUSTNAME, P.&quot;PROJNO&quot;, E.ENAME;
Through a combination of views and synonyms, using the following SQL statements,
the process of distributed queries is transparent:
CREATE SYNONYM ORDERS FOR ORDERS@DB2;
CREATE SYNONYM PROJECTS FOR &quot;PROJECTS&quot;@SYBS;
CREATE VIEW DETAILS (CUSTNAME,PROJNO,ENAME,SPEND)
AS
SELECT O.CUSTNAME, P.&quot;PROJNO&quot;, E.ENAME, SUM(E.RATE*P.&quot;HOURS&quot;)
SPEND
FROM ORDERS O, EMP E, PROJECTS P
WHERE O.PROJNO = P.&quot;PROJNO&quot;
AND P.&quot;EMPNO&quot; = E.EMPNO
GROUP BY O.CUSTNAME, P.&quot;PROJNO&quot;, E.ENAME;
Use the following SQL statement to retrieve information from the data stores in one
statement:
SELECT * FROM DETAILS;
The statement retrieves the following table:
CUSTNAME
-------ABC Co.
ABC Co.
XYZ Inc.
XYZ Inc.
PROJNO
-----1
1
2
2
ENAME
----Jones
Smith
Jones
Smith
SPEND
----400
180
400
180
4.8 Copying Data from the Oracle Database Server to the Non-Oracle
Database System
Heterogeneous Services supports callback links. This enables SQL statements like the
following to be executed:
INSERT INTO table_name@dblink SELECT column_list FROM table_name;
Even though Heterogeneous Services supports the callback functionality, not all
gateways have implemented it. If the gateway that you are using has not implemented
this functionality, the preceding INSERT statement returns the following error
message:
ORA-02025: All tables in the SQL statement must be at the remote database
4-12 Oracle Database Heterogeneous Connectivity User's Guide
Copying Data from the Non-Oracle Database System to the Oracle Database Server
See Also: Your gateway documentation for information about
support for callback links
For gateways that do not support callback links, you can use the SQL*Plus COPY
command. The syntax is as follows:
COPY FROM username/password@db_name INSERT destination_table USING query;
The following example selects all rows from the local Oracle emp table, inserts them
into the emp table on the non-Oracle database, and commits the transaction:
COPY FROM SCOTT/TIGER@inst1 INSERT EMP@remote_db USING SELECT * FROM EMP;
The COPY command supports the APPEND, CREATE, INSERT, and REPLACE options.
However, INSERT is the only option supported when copying to non-Oracle
databases. The SQL*Plus COPY command does not support copying to tables with
lowercase table names. Use the following PL/SQL syntax with lowercase table names:
DECLARE
v1 oracle_table.column1%TYPE;
v2 oracle_table.column2%TYPE;
v3 oracle_table.column3%TYPE;
.
.
.
CURSOR cursor_name IS SELECT * FROM oracle_table;
BEGIN
OPEN cursor_name;
LOOP
FETCH cursor_name INTO v1, v2, v3, ... ;
EXIT WHEN cursor_name%NOTFOUND;
INSERT INTO destination_table VALUES (v1, v2, v3, ...);
END LOOP;
CLOSE cursor_name;
END;
SQL*Plus User's Guide and Reference for more
information about the COPY command
See Also:
4.9 Copying Data from the Non-Oracle Database System to the Oracle
Database Server
The CREATE TABLE statement lets you copy data from a non-Oracle database to the
Oracle database. To create a table on the local database and insert rows from the
non-Oracle table, use the following syntax:
CREATE TABLE table_name AS query;
The following example creates the table emp in the local Oracle database and inserts
the rows from the EMP table of the non-Oracle database:
CREATE TABLE table1 AS SELECT * FROM &quot;EMP&quot;@remote_db;
Using Heterogeneous Services Agents 4-13
Using Heterogeneous Services Data Dictionary Views
Alternatively, you can use the SQL*Plus COPY command to copy data from the
non-Oracle database to the Oracle database server.
SQL*Plus User's Guide and Reference for more
information about the COPY command
See Also:
4.10 Using Heterogeneous Services Data Dictionary Views
You can use the Heterogeneous Services data dictionary views to access information
about Heterogeneous Services. This section addresses the following topics:
■
Understanding the Types of Views
■
Understanding the Sources of Data Dictionary Information
■
Using the General Views
■
Using the Transaction Service Views
■
Using the SQL Service Views
4.10.1 Understanding the Types of Views
The Heterogeneous Services data dictionary views, whose names all begin with the
HS_ prefix, can be divided into the following categories:
■
General views
■
Views used for the transaction service
■
Views used for the SQL service
Most of the data dictionary views are defined for both classes and instances. For most
types of data there is a *_CLASS view and a *_INST view. See Table 4–1 for additional
details.
Table 4–1
Data Dictionary Views for Heterogeneous Services
View
Type
Identifies
HS_BASE_CAPS
SQL service
All capabilities supported by Heterogeneous Services
HS_BASE_DD
SQL service
All data dictionary translation table names supported by
Heterogeneous Services
HS_CLASS_CAPS
Transaction service,
SQL service
Capabilities for each class
HS_CLASS_DD
SQL service
Data dictionary translations for each class
HS_CLASS_INIT
General
Initialization parameters for each class
HS_FDS_CLASS
General
Classes accessible from the Oracle server
HS_FDS_INST
General
Instances accessible from the Oracle server
HS_INST_CAPS
Transaction service,
SQL service
Capabilities for each instance (if set up by the DBA)
HS_INST_DD
SQL service
Data dictionary translations for each class (if set up by the
DBA)
HS_INST_INIT
General
Initialization parameters for each instance (if set up by the
DBA)
HS_BULK
Data dictionary view to keep track of internal objects
created with bulk load procedures.
4-14 Oracle Database Heterogeneous Connectivity User's Guide
Using Heterogeneous Services Data Dictionary Views
Like all Oracle data dictionary tables, these views are read-only. Do not change the
content of any of the underlying tables.
4.10.2 Understanding the Sources of Data Dictionary Information
The values used for data dictionary content in any particular connection on a
Heterogeneous Services database link can come from any of the following sources, in
order of precedence:
■
■
■
Instance information uploaded by the connected Heterogeneous Services agent at
the start of the session. This information overrides corresponding content in the
Oracle data dictionary, but is never stored into the Oracle data dictionary.
Instance information stored in the Oracle data dictionary. This data overrides any
corresponding content for the connected class.
Class information stored in the Oracle data dictionary.
If the Oracle database server runs with the HS_AUTOREGISTER server initialization
parameter set to FALSE, then information is not stored automatically in the Oracle
data dictionary. The equivalent data is uploaded by the Heterogeneous Services agent
on a connection-specific basis each time a connection is made, with any
instance-specific information taking precedence over class information.
It is not possible to determine positively what capabilities
and what data dictionary translations are in use for a given session
due to the possibility that an agent can upload instance
information.
Note:
You can determine the values of Heterogeneous Services initialization parameters by
querying the VALUE column of the V$HS_PARAMETER view. Note that the VALUE
column of V$HS_PARAMETER truncates the actual initialization parameter value from
a maximum of 255 characters to a maximum of 64 characters. It truncates the
parameter name from a maximum of 64 characters to a maximum of 30 characters.
4.10.3 Using the General Views
The views that are common for all services are as follows:
View
Contains
HS_FDS_CLASS
Names of the classes that are uploaded into the Oracle data
dictionary
HS_FDS_INST
Names of the instances that are uploaded into the Oracle data
dictionary
HS_CLASS_INIT
Information about the Heterogeneous Services initialization
parameters
For example, you can access multiple Sybase gateways from an Oracle database server.
After accessing the gateways for the first time, the information uploaded into the
Oracle database server could appear as follows:
SQL&gt; SELECT * FROM HS_FDS_CLASS;
FDS_CLASS_NAME
FDS_CLASS_COMMENTS
FDS_CLASS_ID
--------------------- ------------------------------ ------------
Using Heterogeneous Services Agents 4-15
Using Heterogeneous Services Data Dictionary Views
Sybase816
Sybase817
Uses Sybase driver, R1.1
Uses Sybase driver, R1.2
1
21
Two classes are uploaded: a class that accesses Sybase816 and a class that accesses
Sybase817. The data dictionary in the Oracle database server now contains capability
information, SQL translations, and data dictionary translations for both Sybase816 and
Sybase817.
The Oracle database server data dictionary also contains instance information in the
HS_FDS_INST view for each non-Oracle system instance that is accessed.
4.10.4 Using the Transaction Service Views
When a non-Oracle system is involved in a distributed transaction, the transaction
capabilities of the non-Oracle system and the agent control whether it can participate
in distributed transactions. Transaction capabilities are stored in the HS_CLASS_CAPS
tables.
The ability of the non-Oracle system and agent to support two-phase commit protocols
is specified by the 2PC type capability, which can specify one of the types shown in the
following table.
Type
Capability
Read-Only (RO)
The non-Oracle system can be queried only with SQL SELECT statements.
Procedure calls are not allowed because procedure calls are assumed to write data.
Single-Site (SS)
The non-Oracle system can handle remote transactions but not distributed
transactions. That is, it cannot participate in the two-phase commit protocol.
Commit Confirm (CC)
The non-Oracle system can participate in distributed transactions. It can
participate in the server's two-phase commit protocol but only as the commit point
site. That is, it cannot prepare data, but it can remember the outcome of a
particular transaction if asked by the global coordinator.
Two-Phase Commit (2PC)
The non-Oracle system can participate in distributed transactions. It can
participate in the server's two-phase commit protocol, as a regular two-phase
commit node, but not as a commit point site. That is, it can prepare data, but it
cannot remember the outcome of a particular transaction if asked to by the global
coordinator.
Two-Phase Commit Confirm The non-Oracle system can participate in distributed transactions. It can
(2PCC)
participate in the server's two-phase commit protocol as a regular two-phase
commit node or as the commit point site. That is, it can prepare data and it can
remember the outcome of a particular transaction if asked by the global
coordinator.
The transaction model supported by the driver and non-Oracle system can be queried
from the HS_CLASS_CAPS Heterogeneous Services data dictionary view.
The following example shows one of the capabilities is of the 2PC type:
SELECT
FROM
WHERE
AND
cap_description, translation
hs_class_caps
cap_description LIKE '2PC%'
fds_class_name LIKE 'SYBASE%';
CAP_DESCRIPTION
TRANSLATION
---------------------------------------- ----------2PC type (RO-SS-CC-PREP/2P-2PCC)
CC
When the non-Oracle system and agent support distributed transactions, the
non-Oracle system is treated like any other Oracle server. When a failure occurs during
4-16 Oracle Database Heterogeneous Connectivity User's Guide
Using Heterogeneous Services Data Dictionary Views
the two-phase commit protocol, the transaction is recovered automatically. If the
failure persists, the in-doubt transaction may need to be manually overridden by the
database administrator.
4.10.5 Using the SQL Service Views
Data dictionary views that are specific for the SQL service contain information about:
■
■
SQL capabilities and SQL translations of the non-Oracle data source
Data dictionary translations to map Oracle data dictionary views to the data
dictionary of the non-Oracle system
This section describes only a portion of the SQL
Service-related capabilities. Because you should never need to alter
these settings for administrative purposes, these capabilities are not
discussed here.
Note:
4.10.5.1 Using Views for Capabilities and Translations
The HS_*_CAPS data dictionary tables contain information about the SQL capabilities
of the non-Oracle data source and required SQL translations. These views specify
whether the non-Oracle data store or the Oracle database server implements certain
SQL language features. If a capability is turned off, then Oracle does not send any SQL
statements to the non-Oracle data source that require this particular capability, but it
still performs postprocessing.
4.10.5.2 Using Views for Data Dictionary Translations
In order to make the non-Oracle system appear similar to an Oracle database server,
Heterogeneous Services connections map a limited set of Oracle data dictionary views
onto the non-Oracle system's data dictionary. This mapping permits applications to
issue queries as if these views belonged to an Oracle data dictionary. Data dictionary
translations make this access possible. These translations are stored in Heterogeneous
Services views whose names have the _DD suffix.
For example, the following SELECT statement transforms into a Sybase query that
retrieves information about emp tables from the Sybase data dictionary table:
SELECT * FROM USER_TABLES@remote_db
WHERE UPPER(TABLE_NAME)='EMP';
Data dictionary tables can be mimicked instead of translated. If a data dictionary
translation is not possible because the non-Oracle data source does not have the
required information in its data dictionary, then Heterogeneous Services causes it to
appear as if the data dictionary table is available, but the table contains no
information.
To retrieve information about which Oracle data dictionary views or tables are
translated or mimicked for the non-Oracle system, connect as user SYS and issue the
following query on the HS_CLASS_DD view:
SELECT DD_TABLE_NAME, TRANSLATION_TYPE
FROM
HS_CLASS_DD
WHERE FDS_CLASS_NAME LIKE 'SYBASE%';
DD_TABLE_NAME
----------------------------ALL_ARGUMENTS
T
M
Using Heterogeneous Services Agents 4-17
Using the Heterogeneous Services Dynamic Performance Views
ALL_CATALOG
ALL_CLUSTERS
ALL_CLUSTER_HASH_EXPRESSIONS
ALL_COLL_TYPES
ALL_COL_COMMENTS
ALL_COL_PRIVS
ALL_COL_PRIVS_MADE
ALL_COL_PRIVS_RECD
...
T
T
M
M
T
M
M
M
The T translation type specifies that a translation exists. When the translation type is M,
the data dictionary table is mimicked.
4.11 Using the Heterogeneous Services Dynamic Performance Views
The Oracle database server stores information about agents, sessions, and parameters.
You can use the dynamic performance views to access this information. This section
contains the following topics:
■
Determining Which Agents Are Running on a Host: V$HS_AGENT View
■
Determining the Open Heterogeneous Services Sessions: V$HS_SESSION View
■
Determining the Heterogeneous Services Parameters: V$HS_PARAMETER View
4.11.1 Determining Which Agents Are Running on a Host: V$HS_AGENT View
The V$HS_AGENT view identifies the set of Heterogeneous Services agents currently
operating on a specified host. Table 4–2 shows the most relevant columns. For a
description of all the columns in the view, see Oracle Database Reference.
Table 4–2
Important Columns in the V$HS_AGENT View
Column
Description
AGENT_ID
Oracle Net session identifier used for connections to agent (listener.ora SID)
MACHINE
Operating system machine name
PROGRAM
Program name of agent
AGENT_TYPE
Type of agent
FDS_CLASS_ID
The ID of the foreign data store class
FDS_INST_ID
The instance name of the foreign data store
4.11.2 Determining the Open Heterogeneous Services Sessions: V$HS_SESSION View
The V$HS_SESSION view shows the sessions for each agent and specifies the database
link that is used. Table 4–3 shows the most relevant columns. For a description of all
the columns in the view, see Oracle Database Reference.
Table 4–3
Important Columns in the V$HS_SESSION View
Column
Description
HS_SESSION_ID
Unique Heterogeneous Services session identifier
4-18 Oracle Database Heterogeneous Connectivity User's Guide
Using the Heterogeneous Services Dynamic Performance Views
Table 4–3 (Cont.) Important Columns in the V$HS_SESSION View
Column
Description
AGENT_ID
Oracle Net session identifier used for connections to agent (listener.ora SID)
DB_LINK
Server database link name used to access the agent NULL means that no database link is
used (for example, when using external procedures)
DB_LINK_OWNER
Owner of the database link in DB_LINK
4.11.3 Determining the Heterogeneous Services Parameters: V$HS_PARAMETER View
The V$HS_PARAMETER view lists the Heterogeneous Services parameters and their
values that are registered in the Oracle database server. Table 4–4 shows the most
relevant columns. For a description of all the columns in the view, see Oracle Database
Reference.
Table 4–4
Important Columns in the V$HS_SESSION View
Column
Description
HS_SESSION_ID
Unique Heterogeneous Services session identifier
PARAMETER
The name of the Heterogeneous Services parameter
VALUE
The value of the Heterogeneous Services parameter
Information about the database link that was used for establishing the distributed
connection, the startup time, and the set of initialization parameters used for the
session is also available. All of the runtime information is derived from dynamically
updated tables.
Using Heterogeneous Services Agents 4-19
Using the Heterogeneous Services Dynamic Performance Views
4-20 Oracle Database Heterogeneous Connectivity User's Guide
5
Performance Recommendations
This chapter suggests ways to optimize distributed SQL statements and improve the
performance of distributed queries.
This chapter includes the following sections:
■
Optimizing Heterogeneous Distributed SQL Statements
■
Optimizing Performance of Distributed Queries
For information about general data transfer performance, see
Section 4.2, &quot;Optimizing Data Transfers Using Bulk Fetch&quot; and
Section 4.3, &quot;Optimizing Data Loads Using Parallel Load&quot;
Note:
5.1 Optimizing Heterogeneous Distributed SQL Statements
When a SQL statement accesses data from non-Oracle systems, it is said to be a
heterogeneous distributed SQL statement. To optimize heterogeneous distributed SQL
statements, follow the same guidelines as for optimizing distributed SQL statements
that access Oracle databases only. However, you must consider that the non-Oracle
system usually does not support all the functions and operators that Oracle supports.
The Oracle Database gateways tell Oracle (at connect time) which functions and
operators they support. If the non-Oracle data source does not support a function or
operator, then Oracle performs that function or operator. In this case, Oracle obtains
the data from the other data source and applies the function or operator locally. This
affects the way in which the SQL statements are decomposed and can affect
performance, especially if Oracle is not on the same computer as the other data source.
However, performance can be improved if you use the bulk fetch and bulk load
features.
5.2 Optimizing Performance of Distributed Queries
You can improve the performance of distributed queries by using the following
strategies:
■
Choose the best SQL statement.
In many cases, there are several SQL statements that can achieve the same result. If
all tables are on the same database, then the difference in performance between
these SQL statements may be minimal. If the tables are located on different
databases, then the difference in performance may be more significant. Also, note
that the best SQL statement may change from one release to the next.
■
Use the query optimizer.
Performance Recommendations
5-1
Optimizing Performance of Distributed Queries
The query optimizer uses indexes on remote tables, considers more execution
plans than the rule-based optimizer, and generally gives better results. With the
query optimizer, performance of distributed queries is generally satisfactory. Only
on rare occasions is it necessary to change SQL statements, create views, or use
procedural code.
■
Use views.
In some situations, views can be used to improve performance of distributed
queries. For example:
■
–
Joining several remote tables on the remote database
–
Sending a different table through the network
–
Retrieve data from the remote table in parallel
Use procedural code.
On rare occasions, it can be more efficient to replace a distributed query by
procedural code, such as a PL/SQL procedure or a precompiler program.
5-2 Oracle Database Heterogeneous Connectivity User's Guide
Index
A
D
agents
Database Gateways, 2-2
Heterogeneous Services
architecture, 2-1
disabling self-registration, 4-8
registering, 4-5, 4-6, 4-7
types of agents, 2-2
Oracle Database Gateway for ODBC, 2-3
application development
Heterogeneous Services
controlling array fetches between non-Oracle
server and agent, 4-4
controlling array fetches between Oracle server
and agent, 4-4
controlling reblocking of array fetches, 4-5
DBMS_HS_PASSTHROUGH package, 3-4
passthrough SQL, 3-4
using bulk fetches, 4-3
using OCI for bulk fetches, 4-4
array fetches, 4-4
agents, 4-4
data dictionary views
Heterogeneous Services, 4-14
data type checking support
for remote-mapped statements, 4-10
DBMS_HS_PASSTHROUGH package, 3-4
list of functions and procedures, 3-5
distributed queries
optimizing performance, 5-1
dynamic performance views
Heterogeneous Services, 4-18
determining open sessions, 4-18
determining which agents are on host,
B
bind queries
executing using passthrough SQL, 3-7
BIND_INOUT_VARIABLE procedure, 3-5, 3-7
BIND_OUT_VARIABLE procedure, 3-5, 3-7
BIND_VARIABLE procedure, 3-5
buffers
multiple rows, 3-8
bulk fetches
optimizing data transfers using, 4-3
C
callback link, 3-15
CLOSE_CURSOR function, 3-5
copying data
from Oracle database server to SQL Server, 4-12
from SQL Server to Oracle database server, 4-13
INSERT statement, 4-13
4-18
E
EXECUTE_IMMEDIATE procedure, 3-5
restrictions, 3-5
EXECUTE_NON_QUERY procedure, 3-5
F
FDS_CLASS, 4-7
FDS_CLASS_VERSION, 4-7
FDS_INST_NAME, 4-8
features
new, xi
FETCH_ROW procedure, 3-5
executing queries using passthrough SQL, 3-7
fetches
bulk, 4-3
optimizing round-trips, 3-8
G
gateways
how they work, 2-6
GET_VALUE procedure,
3-5, 3-7
H
Heterogeneous Services
agent registration, 4-5
avoiding configuration mismatches, 4-6
disabling, 4-8
enabling, 4-6
Index-1
self-registration, 4-7
application development
controlling array fetches between non-Oracle
server and agent, 4-4
controlling array fetches between Oracle server
and agent, 4-4
controlling reblocking of array fetches, 4-5
DBMS_HS_PASSTHROUGH package, 3-4
passthrough SQL, 3-4
using bulk fetches, 4-3
using OCI for bulk fetches, 4-4
data dictionary views, 4-14
types, 4-14
understanding sources, 4-15
using general views, 4-15
using SQL service views, 4-17
using transaction service views, 4-16
dynamic performance views, 4-18
V$HS_AGENT view, 4-18
V$HS_SESSION view, 4-18
initialization parameters, 2-4, 4-1
SQL service, 2-3
transaction service, 2-3
HS_AUTOREGISTER initialization parameter
using to enable agent self-registration, 4-8
HS_BASE_CAPS view, 4-14
HS_BASE_DD view, 4-14
HS_BULK view, 4-14
HS_CLASS_CAPS view, 4-14
HS_CLASS_DD view, 4-14
HS_CLASS_INIT view, 4-14
HS_FDS_CLASS view, 4-14
HS_FDS_FETCH_ROWS initialization
parameter, 4-4
HS_FDS_INST view, 4-14
HS_INST_CAPS view, 4-14
HS_INST_DD view, 4-14
HS_INST_INIT view, 4-14
HS_RPC_FETCH_REBLOCKING initialization
parameter, 4-5
HS_RPC_FETCH_SIZE initialization parameter, 4-4,
4-5
M
I
Q
information integration
benefits of Oracle solutions, 1-3
challenges, 1-1
how Oracle addresses, 1-2
Messaging Gateway, 1-3
Open System Interfaces, 1-3
Oracle Streams, 1-2
initialization parameters
Heterogeneous Services (HS), 2-4, 4-1
initialization parameters (HS)
common to all gateways, 4-1
purpose, 2-4
queries
passthrough SQL, 3-7
Messaging Gateway
defined, 1-3
multiple rows
buffering, 3-8
O
OCI
optimizing data transfers using, 4-4
Open System Interfaces
defined, 1-3
OPEN_CURSOR procedure, 3-5
Oracle Database Gateway for ODBC
Heterogeneous Services, 2-3
Oracle Database gateways
optimizing SQL statements, 5-1
Oracle database server
SQL construct processing, 4-9
Oracle Net Services listener, 2-2
Oracle precompiler
optimizing data transfers using, 4-4
Oracle Streams
defined, 1-2
using for heterogeneous connectivity, 3-2
OUT bind variables, 3-7
P
PARSE procedure, 3-5
passthrough SQL
avoiding SQL interpretation, 3-4
executing statements, 3-5
non-queries, 3-5
queries, 3-7
with bind variables, 3-5
with IN bind variables, 3-6
with IN OUT bind variables, 3-7
with OUT bind variables, 3-7
implications of using, 3-4
overview, 3-4
restrictions, 3-4
R
reblocking, 4-5
remote-mapped statements
and data type checking support,
rows
buffering multiple, 3-8
S
SQL capabilities
data dictionary tables, 4-17
Index-2
4-10
SQL service
data dictionary views, 2-6, 4-14
Heterogeneous Services, 2-3
views
Heterogeneous Services, 4-17
SQL statements
optimizing distributed, 5-1
Synonyms, 4-11
T
transaction service
Heterogeneous Services, 2-3
views
Heterogeneous Services, 4-16
U
user-defined functions
executing on non-Oracle database, 4-10
V
variables
bind, 3-5
Index-3
Index-4
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