A fix is available
APAR status
Closed as program error.
Error description
R-scan access path chosen over multi-index access for a table which qualifies for NPGTHRSH behavior.
Local fix
Problem summary
**************************************************************** * USERS AFFECTED: * * All DB2 for z/OS users of VOLATILE tables or the NPGTHRSH * * zparm. * **************************************************************** * PROBLEM DESCRIPTION: * * For a table defined with the VOLATILE * * attribute, or a table that qualifies * * for NPGTHRSH rules, the DB2 Optimizer * * may sometimes choose a table space * * scan or non-matching index scan rather * * than matching index access that uses * * multiple index ORing, when multiple * * index ORing is the only matching index * * access available. * * * * This can occur when the matching * * predicates used for index ORing * * are estimated to not provide * * sufficient filtering of the table. * * * * Filtering estimates, however, for * * tables defined as VOLATILE or tables * * that qualify for NPGTHRSH rules should * * not be used to disable matching index * * access through a multi-index access * * path, because those estimates may not * * be accurate. * **************************************************************** * RECOMMENDATION: * **************************************************************** The DB2 Optimizer may choose a table space scan over matching index access involving index OR'ing, for tables that have the VOLATILE attribute, or tables that qualify for NPGTHRSH rules. This can occur when the matching predicates used in the index OR'ing plan are estimated to provide insufficient filtering of the table. This can result in a table space scan or non-matching index scan being done instead of doing matching index access by OR'ing multiple indexes.
Problem conclusion
The rules for VOLATILE tables and NPGTHRSH tables are changed to allow matching index access involving index ORing to be selected over table space scan and non-matching index scan regardless of the estimated filtering of the matching predicates. Matching single index access is preferred over matching index ORing access regardless of how many matching predicates are involved in the competing plans. Additional Keywords: SQLACCESSPATH SQLPERFORMANCE SQLOR MIDX
Temporary fix
Comments
APAR Information
APAR number
PI71368
Reported component name
DB2 OS/390 & Z/
Reported component ID
5740XYR00
Reported release
C10
Status
CLOSED PER
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2016-10-26
Closed date
2017-02-02
Last modified date
2017-04-20
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
UI44411
Modules/Macros
DSNXOCSC DSNXOGCM
Fix information
Fixed component name
DB2 OS/390 & Z/
Fixed component ID
5740XYR00
Applicable component levels
RC10 PSY UI44411
UP17/02/21 P F702
Fix is available
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Document Information
Modified date:
20 April 2017