Watch out for these 12c bugs

A quick little post, but I think this is an important one as most people have upgraded/plan to upgrade to 12c

Oracle performance can be impacted by Oracle itself. People are often too quick to jump to the conclusion that bad performance is the result of a bug. That does not mean that there aren't situations where bugs do occur.

In 12c I have seen a couple of instances where bugs are using a noticable amount of system time. This consumes CPU cycles and potentially takes away time from other processes.

Looking at top statements and top wait events can lead to identifying potential bugs. With the 12c bugs being encountered they can be seen using AWR, ASH, or queries against system views to identify the top statements by Elapsed Time or other key metrics.

Once these key consumers of time are identified it is worth the effort to perform a quick search on My Oracle Support to see if there are known issues associated with this issue. There may be a patch or workaround identified that will resolve the bug or "performance feature".

A couple of examples seen recently are related to SQL Ids frjd8zfy2jfdq and 47r1y8yn34jmj. There are a couple of 12c patches which can improve this activity.

See
Frequent Execution of Recursive Sql Metrics Collector SQL_ID "frjd8zfy2jfdq" in 12.1.0.2 (Doc ID 2059121.1)
Higher CPU and Slow Performance after Migration to 12c with Top Sql as SELECT DEFAULT$ FROM COL$ WHERE ROWID=:1 (Doc ID 2013851.1)