(Originally posted 2006-05-22.)
Here are a couple more SQL processing APARs.
APAR PK22814 for Version 8 ESTIMATED SUBQUERY COST IS TOO HIGH WITH SORT MERGE JOIN.
The APAR text says Correlated subquery cost is over-estimated for sort merge join. A well-performing sort merge join plan might not be chosen by DB2. Correlated subquery cost can be overestimated for sort merge join. This may cause a sort merge join plan that performs well to be overlooked by DB2. The cost calculations for sort merge join with a correlated subquery are adjusted to produce a more accurate estimate. Good sort merge join plans can now be chosen for better query performance.
APAR PK23495 for Version 8 SOME PREDICATES ARE NOT BEING PROPERLY PUSHED DOWN INTO VIEWS.
From the APAR text: Slow access path is chosen for an SQL statement referencing a view or a table expression that contains an outer join, because the predicates are not being properly pushed down.
The bind time code in DB2 is modified to correct the incomplete predicate push down.
Mainframe, Performance, Topics 