[Mondrian] Calculated Member Solve Order&AggregateFunctionHandling

Thu May 22 15:56:33 EDT 2008

Submitted as change 11099. Thanks for the contribution, Timothy.

I made the default behavior scoped - i.e. compatible with AS 2005, different
than behavior in 3.0.3 and earlier. I don't expect many applications to be
affected, but the property mondrian.rolap.SolveOrderMode exists if anyone
needs backwards compatibility.

Timothy, Can you explain why
_testOverrideOverCubeMemberHappensWithScopeIsolation is still disabled?

Julian

  _____  

From: mondrian-bounces at pentaho.org [mailto:mondrian-bounces at pentaho.org] On
Behalf Of timothy.lambert at thomsonreuters.com
Sent: Wednesday, May 21, 2008 8:57 AM
To: mondrian at pentaho.org
Subject: RE: [Mondrian] Calculated Member Solve
Order&AggregateFunctionHandling 

See my comments below preceded with ">>>"

  _____  

From: mondrian-bounces at pentaho.org [mailto:mondrian-bounces at pentaho.org] On
Behalf Of Julian Hyde
Sent: Monday, May 19, 2008 8:39 PM
To: 'Mondrian developer mailing list'
Subject: RE: [Mondrian] Calculated Member Solve Order
&AggregateFunctionHandling 

Timothy,

The change looks good, but you need to tie up a few loose ends to be tied up
before I can accept the contribution:

1. The unit test cases need some work. I enabled the tests in
SolveOrderScopeIsolationTest, and most worked if I preceded them with a
check that SolveOrderMode==scoped. But
testOverrideOverCubeMemberHappensWithScopeIsolation still gives errors;
can't figure out whether it's to do with case sensitivity.

>>> I think that the intent of this test was for the AS2005
"SCOPE_ISOLATION=CUBE" MDX property testing.  Since Mondrian isn't
supporting that property with this contribution, I didn't spend the time
figuring out the problem with this test case.  I left the test case in but
preceded the method with an underscore to prevent it from running.

And, can you create some cases that test the behavior when
SolveOrderMode==absolute. This will be especially important when scoped
becomes the default behavior. Maybe make each test case into an 'if ...
else' with alternative outputs.

>>> I implemented your suggestion of alternative output handling when run
with 'absolute'.

2. The description of the property in mondrian.properties and
MondrianProperties.java needs a little more information, because the average
DBA would not know what SS2K behavior was (or SS2K was, for that matter).
The information in your email below would do just fine.

>>> Done.

3. Please put the same property information into configuration.html.

>>> Done.

4. For future changes, please keep those lines to 80 characters, and use <p>
to delimit paragraphs in javadoc.

>>> Will do.

See attached a new change list with my modifications.

>>> Attached are my new changes along with your additions.

All,

Any opinions what should be the default behavior? I'm inclined to think that
mondrian should use scoped solve-order (like Analysis Services 2005) by
default.

Julian

  _____  

From: mondrian-bounces at pentaho.org [mailto:mondrian-bounces at pentaho.org] On
Behalf Of Lambert, Timothy
Sent: Monday, May 12, 2008 3:05 PM
To: mondrian at pentaho.org
Subject: [Mondrian] Calculated Member Solve Order & Aggregate
FunctionHandling 

Calculated Member Solve Order & Aggregate Function Handling 

SSAS2005 vs. SSAS2000 vs. Mondrian

Background

This proposal was seeded by the R&D of others.

Following are links to some of that work.

http://forums.pentaho.org/showthread.php?t=60654

http://777eisenhower.blogspot.com/2008/03/analysis-services-2000-vs-2005.htm
l

SOLVE_ORDER Calculated Member Property

Definition:  The order of evaluation (from highest to lowest solve order)
and calculation (from lowest to highest solve order) for calculated members,
custom members, custom rollup formulas, and calculated cells in a single
calculation pass of a multidimensional cube. Solve order is used to
determine formula precedence when calculating values for cells in
multidimensional cubes, but only within a single calculation pass.

SSAS2000 Behavior:  The SOLVE_ORDER value is absolute regardless of where it
is defined; e.g. a query defined calculated member with a SOLVE_ORDER of 1
always takes precedence over a cube defined value of 2.

SSAS2005 Behavior:  By default, cube calculated members are resolved before
any session scope calculated members, and session scope members are resolved
before any query defined calculation.  The SOLVE_ORDER value only applies
within the scope in which it was defined.  

Achieving SSAS2000 Behavior on SSAS2005:  Using the SCOPE_ISOLATION=CUBE
property in a query calculated member definition will put the query defined
member into cube scope.  So effectively solve_order is treated like an
SSAS2000 absolute value since all members are treated as if they were
defined in the same scope.

Aggregate Function

Definition:  Returns a number that is calculated by aggregating over the
cells returned by the set expression.  

The Aggregation function is designed to be used against base measures.

SSAS2000 Behavior:  The SOLVE_ORDER value must be manually applied such that
aggregate values are solved before other related calculated members.

SSAS2005 Behavior:  The aggregate function is always applied to base
members; i.e. as if solve_order was defined to be the lowest value in a
given evaluation in a SSAS2000 sense.

Current Mondrian Behavior

In regard to solve_order and Aggregate function handling, Mondrian behaves
like SSAS2000.

During the evaluation of a given cell, if there are multiple calculated
members in the evaluation context then the member with the highest
solve_order is evaluated.  The other calculated members with lower
solve_order values stay within the evaluation context, and are evaluated
during the processing of the calculated member with the higher solve_order.

Through this recursive process, the calculated members with lower
solve_order values get calculated before those with higher values.

Mondrian Issue

For use with certain reporting clients (e.g. Cognos), it is better for
Mondrian to behave like SSAS2005 rather than SSAS2000 in regard to solve
order and aggregate function evaluation.  

Note that some reporting clients (e.g. Cognos) do not take advantage of the
SSAS2005 SCOPE_ISOLATION property, so support for it is not considered
critically important.

Proposed Mondrian Changes

High Level

The proposal involves enhancing Mondrian to optionally behave like SSAS2005
rather than SSAS2000 in regard to solve order.  

The option is controlled using the MondrianProperties entry
SolveOrderMode=absolute|scoped.  The current Mondrian solve order behavior
remains the default; 'absolute'.  The SSAS2005 behavior can be turned on
with the value of 'scoped'.  One can achieve SSAS2005 SCOPE_ISOLATION=CUBE
semantics by using 'absolute' mode.

While preserving old behavior as a default is usually desirable, in this
case it is recommended that Mondrian adopt the SSAS2005 behavior as the
default.

The implementation of the proposal is based on the same sort of logic one
uses when manually applying the solve_order property to get the desired
SSAS2005-like behavior with current Mondrian.

The 'scoped' solve order mode code determines the highest solve order based
on.

-   If the calculated member is involved with an aggregate function.  

Aggregation function based calculations are calculated first.

-   The location of the calculated member definition; i.e. its scope. 

Cube scope members are calculated after Aggregate function based
calculations.  

Query scope members are calculated after cube scope calculations.

-   The solve_order property.  

This property is only used to order calculations within a given scope.

Code Changes

Attached to this email - the archive was built with the packChange script.

The RolapEvaluator.peekCalcMember method now invokes one of two methods for
determining the highest solve order for two or more calculated members.
One of these methods implements the "absolute" algorithm and the other
implements the "scoped" algorithm.

Determining cube and query scope is easy since there is an already defined
class method for determining if a member is defined in a query.  If it's not
defined in the query then it must be defined in the cube.

Determining relative solve_order is also trivial since that property is
readily available for a given calculated member.

Determining if the member is part of an aggregate function is a little more
difficult.  There are (at least) two ways to go about this.

In the proposed solution, there is a new RolapEvaluator method that
traverses the expression graph associated with a calculated member
explicitly looking for an aggregate function.

An alternate solution performed a full evaluation of the calculated member
in order to look for an aggregate function.  After the evaluation, a flag
was checked to see if an aggregate function was found.

Unit Tests

A JUnit test (SolveOrderScopeIsolationTest) was recently contributed to the
Mondrian project.  These test cases expect AS2005 behavior and as such fail
with the current Mondrian.  So this test is not normally setup to run with
the regular regression suite.  

When this test is enabled, the proposed implementation with the new AS2005
solve order behavior passes all test cases.  

Note there is one exception in which Mondrian fails regardless of
SolveOrderMode.  There seems to be an MDX syntax problem in one of the test
cases.

Also note there is one test case that passes for both the old and new
behavior.

There is another test case that passes for current Mondrian but fails for
the new solve order behavior.  The test case is
Mondrian.test.NamedSetTest.testOrderedNamedSet.  The test case explicitly
expects SSAS2000 behavior and as such should fail with the new AS2005
behavior.

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