12c Regressed SQL - Unexplained Buffer Sort Used
Last updated on NOVEMBER 02, 2016
Applies to:Oracle Database - Enterprise Edition - Version 184.108.40.206 and later
Information in this document applies to any platform.
After migrating from 11g to 220.127.116.11, CTAS statement has a strange plan in 12c compared with 11g.
This is a CTAS that is executed using DEFAULT parallelism. Both the 11g and 12c databases are running on the same host with cpu_count set to 32 (default value).
in 18.104.22.168, the CTAS statement takes 7.5 minutes.
In 22.214.171.124, the same CTAS takes 13 minutes.
What you see in 12c is now we have a “PX Deq: Table Q Ref” event. So, we have slaves waiting a long time for something to happen.
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