Sample Slide

Sample Slide
Advanced Rules & Feeders
Outline
•Rules Basics
•Feeders Completeness
•Performance
•Rules vs. TI
1 Rule Basics

TM1 Calculations

Cell Calculations

View Calculations

Feeders Basics
1.1 TM1 Calculations
 Calculations are On Request and Recursive
 Cell by Cell Calculation
 View Calculation
 Intermediate results are stored for re-use.
1.1 TM1 Calculations (cont’d)
Why Calculations on Demand: Real Time Performance.
 OLAP Geometric Explosion - One change affects many
cells.
 Example: 10 Dimensions, 3 Levels each. Change one
leaf cell affects 310 -1 calculated cells = 59,048.
 In-memory architecture and special algorithms permit
fast last-minute calculations.
 Only relevant cells are calculated.
1.2 Cell Calculations
Get Cell
Consolidation
Go through
nonempty cells
Get Cells
Accumulate
Determine
Cell Type
Simple Cell
Get Value
from Cube
Done
Rule
Interpret
Expression
Get Cells
Calculate
Expression
1.3 Views Calculations
 View consolidations are calculated “wholesale” using
an algorithm called “Stargate”.
 Performance ~ n times faster than cell by cell, where
n is the number of cells. Get n for ~ the price of 1.
1.3 Rules in Views
When rule

Is evaluated in the context of a view

Requests a consolidated cell

Cell some cell members occur in the axes of the
view.
Then
Consolidation is done with Stargate and result saved
for use by other cells in view.
1.3 Storage of Views
 VMT and VMM control storage of views.
 When view requested is included in stored view,
stored view is used.
 When view requested overlaps stored view, the axes
are “joined” and a new expanded view is constructed
and stored.
1.4 Feeders Basics

Consolidation speed derives from “skipping” empty
areas of cube.

In most applications “density” is < 10-6.

Thus need to “tag” cells that have values
calculated by rules.

Otherwise calculation could take more than 1
million times longer. The price of forgetting
SKIPCHECK!
1.4 Feeders Basics – Q&A



Are there any effects of feeders if SKIPCHEK is forgotten?

No, feeders are still done, but ignored. Instead every
cell is evaluated.
Would that happen if feeder and rules are in different
cubes?

Same
Even an empty rule file switches sparsity algorithm off?

Yes - VERY IMPORTANT
1.4 Feeders Basics (cont’d)
Feeder statements have the form:

TriggerRange => Target.
Feeders are triggered by data input to an empty
cell



If A = k * B - Feed A from B.

If A = B +C - Feed from B AND C

If A = B * C - Feed from either B OR C
Feeders propagate recursively.
1.4 Feeders Basics – Q&A
•
Concerning B*C, should you feed from B or from C?
–
•
from whichever is more likely to be zero.
If Cube X feeds Y, and Y feeds Z, would it make sense to
feed Z directly from X
– No, because rules will be hard to understand and
maintain, and you still have to feed Y
•
If what if X, Y and Z are portions of the same cube?
– Answer unchanged
•
If Y has rules that use values from X, where are feeders
written?
– always in the source cube, i.e., in X.
1.4 Feeders Basics (Cont’d)
 Zero Suppression

Feeders are necessary for proper zero suppression.

Even if you do not use SKIPCHECK, zero
suppression will not work without feeders.
 Feeding Strings

String cells are normally not fed.

Must use FEEDSTRINGS statement to enable.
1.4 Feeders Basics (Cont’d)
 Feeding from Strings

Feeders from string cells re-fire whenever value
changes.

Re-fire does not propagate – if target cell is
already fed (string or numeric) it will not fire.

Watch out when feeding from strings – Entering a
string at a consolidated level will cause
overfeeding.
1.4 Feeders Basics (Cont’d)
Feeding from and to consolidations

To consolidation: feed all leaf components. Can
result in overfeeding.

From consolidation: feed from each leaf
component.
1.4 Feeders Basics - Case
Q. What if Y uses values from X, and the time
dimension in X (Month) goes down to months, but the
one in Y (Year) only down to years?
A. The months in X must feed the corresponding years
in Y. However, you cannot write !Year on the right
had side. You must use ELPAR or preferably an
attribute that maps month to year.
2 Feeders Completeness

Locating Missing Feeders

String-Driven Feeders
2.1 Locating Missing Feeders
 Using Rules Tracer
 Needle in a haystack. Must examine every cell.
 Judiciously look at subareas.
2.2 String Driven Feeders

Strings parameters are often used to direct
calculations an feeders.

Care must be used to define feeders so they
re-trigger when the string parameters are
changed.
2.2 String Driven Feeders – A common trap
Feeders are often written in such a way that the one of
the elements in the target (written using a db()
expression) are specified by a string stored in some
cube.
TriggerRange => DB( …, DB(stringcubecell, ...), …)
The problem with this is that if the string in question is
changed, the feeder will not re-fire because the
cells in TriggerRange are already populated. And
the consolidations will be WRONG.
To correct the situation, the trigger of the feeder must
use the string in question which, as mentioned
before, will fire whenever the string is changed.
3. Performance

Missing SKIPCHEKs

Overfeeding

Other
3.1 Missing Skipchecks
 Symptom: Very slow performance
 Approach:
 Check
 Put
 An
all rule files and put them in.
in appropriate feeders
empty rule will cause sparse consolidations
to be turned off and slow performance
3.2 Overfeeding
•
Why worry about overfeeding?
•
Locating Overfeeds
•
Conditional Feeders
3.2.1 Why worry about overfeeding?
•
Slow cube loading.
•
Unnecessary memory consumption.
•
Slow Performance.
Which is the most significant?
3.2.2 Technique for locating Overfeeds
 Create cube OVERFEED with the same dimensions as
subject cube.
 Add rule to OVERFEED as follows:
SKIPCHECK;
[]=N:IF(DB(’01Basic’,!dim1 , !dim2, ...)=0,1,0);
 Add feeder to subject cube as follows:
[]=>DB(‘OVERFEED’, !dim1 , !dim2, ...);
3.2.3.1 Conditional Feeders Basics
 Purpose - to minimize number of “overfeeds”.
 Trick: Write if expression for the target cube name
that yields a blank when feeders are NOT to take
place.
 Classic example:
A=B*C
B feeds A if C is nonzero
C feeds A if B is nonzero
3.2.3.2 Different Dimensionalities
AxB
Conditional
=
*
A
Baux
B
3.2.3.2 Different Dimensionalities - Example
To Calculate:
Commission( Product, SalesPerson, Time) = Sales( Product,
SalesPerson, Time) * CommissionRate( Product, Time)
Create
CommissionRateAux(Product, SalesPerson, Time)
In CommissionRate:
[] => DB(‘CommissionRateAux’, !Product, ‘All Salespersons’, !Time);
In CommissionRateAux:
[] => DB( IF( DB(‘Sales’, !Product, !SalesPerson, !Time) = 0,
‘’,‘Commission’), !Product, !SalesPerson, !Time);
In Sales:
[] => DB( IF( DB(‘CommissionRate’, !Product, !Time) = 0.
‘’,‘Commission’), !Product, !SalesPerson, !Time);
3.3 Other Methods
• Avoiding Long Expressions
• Avoiding Ratio Feeders
• Avoiding Matrix Multiplication Feeders
• Freezing Rules
• Miscellaneous
3.3.1 Avoiding Long Expressions
 Complex expression (with identical data) used for
multiple cells - Calculation is done over and over.
 Approach: “Factor out” by defining calculation as cells
in auxiliary cube.
3.3.2 Avoiding Ratio Feeders
Ratio calculations such as:
[‘Sales Percent of Year'] =
['Sales']\['Year','Sales']*100;
apply at all levels of hierarchy. I.e., rule is not
preceded by N: or C:
Therefore no feeders are needed for consolidations
because leaf values are never consolidated. Problem
is, how to support zero suppression.
Answer: Define “Sales Percent of Year” as a
consolidation of “Sales”. This effectively acts as a
feeder from “Sales”, but costs no memory.
3.3.3 Avoiding Matrix Multiplication Feeders
d2
AxB
=
A
*
d1
d1
d3
d2
B
d3
d2
3.3.3 Case– “Multicurrency” Company
 Large reporting cube
 Need all data in 12 currencies
 Long time to load
 Hardware memory limits exceeded
 Client not happy
3.3.3 Approach
 Currency rate varies only with TIME - not with other
dimensions.
 Can express currency rule for both “C” and “N” cells.
 All consolidations would be right except TIME.
 Express TIME consolidation using rules
(ConsolidateChildren)
 No feeders needed.
 But need to express calculated currencies as
consolidation of base currency in order to support
zero suppression.
3.3.4 Freezing Rules
 One way to improve performance of a TM1
application is to “freeze” rule calculated values for
periods or versions that are not subject to change.
Typically history or frozen scenarios.
 This way, the cells thus frozen need not be
recalculated when other values in the same cube are
updated.
3.3.4 Freezing Rules - Method

User selects a cube, a dimension within the cube,
and leaf members in the dimension to be frozen.

The leaf values for those members are extracted
and output to an ASCII file, including leaf values
calculated by rules.

The rules that apply to leaf cells are deactivated for
the members frozen.

The values that were output to the ASCII file are reimported into the cube.
3.3.4 Freezing Rules - Continued
In order to disable the rules for the frozen members
automatically, rather than editing the rule file, do as
follows:
 Put disabled members in a parallel dimension.
 Put rules that do not apply only to leaf cells at the
beginning.
 Follow it by a conditional expression of the form:
 [] = IF( DIMIX(‘Dimx_Freeze', !Dimx) =0, CONTINUE,
STET);
 One for each dimension with frozen members.
3.3.5 Miscellaneous
 Inadequate optimization of consolidations in rules
(rare cases).

Rules not taking full advantage of “Stargate”.

Can easily make performance worse by a factor of
10.

Report to support / development.
4 Rules vs. TI
Rules
TI
Ease of writing / maintaining
+ Declarative expression more
intuitive for user.
- Feeders a challenge for all.
- Limited ability for complex
calculations.
+ Procedural calculations more
familiar to developers.
- Requires additional setup to
trigger calculations.
+ Able to handle iterative
calculations.
Error proneness
-Locating incomplete feeders
-Value-directed feeders
- User must remember to
trigger.
+ Procedural calculations
easier to test and fix.
Performance
+ Only necessary cells are
calculated
- Invalidated when values
change.
O Calculation speed
comparable
- Must calculate all cells. No
trigger based on change.
O Calculation speed
comparable
Dynamism
+ Dynamic - always up to date
- Not Dynamic
Memory
O No significant difference
O No significant difference
Thank You
Advanced Rules and Feeders
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