[Mondrian] caching problem in latest Mondrian code
John V. Sichi
jsichi at gmail.com
Sat Apr 5 03:40:36 EDT 2008
After hitting the deadlock, we went ahead with analysis on the
single-thread portion of the LucidEra perf test suite, which had
completed before the concurrency portion where the deadlock occurred.
The results showed significant degradation for just about every report,
so I poked around with some of the unit tests. The MDX for TestCase
testsrc/main/mondrian/test/clearview/GrandTotalTest.ref.xml exhibits the
problem (takes 23 seconds to run, compared to 18 seconds for our old
stable version). I turned on SQL tracing, and saw a lot more SQL than
in the old version. In particular, I saw the 'Drink' query below over
and over, which made me think the member caching is broken.
Here's what I see happening while tracing.
SmartMemberReader.getMemberChildren first calls
cacheHelper.getChildrenFromCache, and doesn't get anything. Further on,
it calls readMemberChildren, which is supposed to call
cacheHelper.putChildren to store them. However, readMemberChildren is
overridden by subclass
RolapCubeHierarchy.RolapCubeHierarchyMemberReader, and its
implementation does *not* call cacheHelper.putChildren at all! Instead,
it calls into rolapCubeCacheHelper.putChildren, but rolapCubeCacheHelper
is a different object (there's a todo at the top of the class for
explaining the distinction). So next time through,
SmartMemberReader.readMemberChildren is going to have to fetch them
again, over and over.
BTW, there's a lot of copy-and-paste between the two implementations of
readMemberChildren; someone might want to do some refactoring.
SQL for cache misses:
select "product_class"."product_department" from "product_class" as
"product_class", "product" as "product", "sales_fact_1997" as
"sales_fact_1997" where "sales_fact_1997"."product_id" =
"product"."product_id" and "product"."product_class_id" =
"product_class"."product_class_id" and "product_class"."product_family"
= 'Drink' and ("product_class"."product_family" = 'Drink') group by
"product_class"."product_department" order by
More information about the Mondrian