APAR status
Closed as fixed if next.
Error description
The optimizer might favour a hash join (HSJOIN) over a nested loop join (NLJOIN) alternative under the following conditions: - the join is on two or more columns - both tables in the join have an index with leading, non-bound key columns that participate in the join - one or more leading columns match in order of the join columns, but not all For example, consider the following query SELECT * FROM T1,T2 WHERE T1.A=T2.A and T1.B=T2.B and T1.C=T2.C and T1.X=1; where index IX1 is defined on T1(X,A,C,B) and index IX2 is defined on T2(A,B,C). The column T1.X is bound to the constant 1 as a result of the predicate "T1.X=1" so for the NLJOIN with IX1 access on the outer and IX2 access on the inner, the leading non-bound columns for both indexes are referenced in the join predicate T1.A=T2.A, but the subsequent columns are not ordered in join column order. Under these conditions, the optimizer might over estimate the cost of the NLJOIN alternative, favouring a possibly worse-performing HSJOIN alternative
Local fix
Create an index on either table, ensuring that the key columns are in join order. Referring to the example in the Error Description, this could be achieved by creating an index on T2(A,C,B).
Problem summary
**************************************************************** * USERS AFFECTED: * * ALL * **************************************************************** * PROBLEM DESCRIPTION: * * See Error Description * **************************************************************** * RECOMMENDATION: * * Upgrade to the level of DB2 Version 9.7 containing fix for * * APAR IC90024 * ****************************************************************
Problem conclusion
Temporary fix
See Local Fix
Comments
APAR Information
APAR number
IV33576
Reported component name
DB2 POFW
Reported component ID
5724N8100
Reported release
950
Status
CLOSED FIN
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt
Submitted date
2012-12-17
Closed date
2013-02-05
Last modified date
2013-02-05
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
IC90024
Fix information
Applicable component levels
R950 PSN
UP
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Document Information
Modified date:
05 February 2013