Potential Ramifications of OPTIMIZER_INDEX_CACHING parameter
(Doc ID 1474966.1)
Last updated on FEBRUARY 21, 2019
Applies to:Oracle Database - Enterprise Edition - Version 10.2.0.4 and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Cloud Exadata Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Information in this document applies to any platform.
A complex query got different execution plans between test and production environment. Statistics are the same in both environments.
- Query performs differently on 2 similar systems (Production/Test)
- Both systems have OPTIMIZER_INDEX_CACHING was set to 100. Default value for this parameter is 0.
- Parameters on the 2 systems are the same except SGA size is 10x larger (30Gb) on the "Bad" (Production) system that the Good (Test) (3Gb)
- Bad plan (Production) shows an additional INDEX SKIP SCAN step in the plan: (table CI_BILL is accessed via an index range scan on index XT033S1)
- Note both plans end up with the same cost.
SGA sizes differ considerably. Whereas in test SGA was only 3GB it was 30GB in production.
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