Instance Caging Not Working As Expected On AIX With SMT4 Enabled

(Doc ID 2342987.1)

Last updated on DECEMBER 28, 2017

Applies to:

Oracle Database - Enterprise Edition - Version 11.2.0.1 and later
IBM AIX on POWER Systems (64-bit)

Symptoms

On IBM AIX and when SMT4 option is enabled, instance caging cannot limit the usage of CPU very well.

For example,

There are 12 cores, and each core has 4 threads, so OS claims that there are 48 CPUs in total.

When enabling Instance Caging and set cpu_count to 24, a consumer group should have maximum utilization limited to 50% OS CPU.

However, the exact CPU utilization of that consumer group can be larger than 50%, and sometimes reached to 100%.

Changes

 SMT4 option is enabled on IBM AIX.

Cause

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