High Waits for 'Log File Sync': Known Issue Checklist for 11.2
Last updated on FEBRUARY 27, 2017
Applies to:Oracle Database - Personal Edition - Version 188.8.131.52 to 184.108.40.206 [Release 11.2]
Oracle Database - Standard Edition - Version 220.127.116.11 to 18.104.22.168 [Release 11.2]
Oracle Database - Enterprise Edition - Version 22.214.171.124 to 126.96.36.199 [Release 11.2]
Information in this document applies to any platform.
High levels of waits for the 'log file sync' wait events are seen.
The 'log file sync' wait event is seen when a foreground process is waiting to be posted by LGWR to acknowledge that their particular buffers in the log buffer have been successfully flushed out to the physical redo logs. Assuming that log writing is working well and IO time is not excessive, most of the 'log file sync' time should be related to IO and there should not be much of a difference between 'log file sync' and 'log file parallel write' wait events.
- When the majority of time is spent on 'log file parallel write' then most likely we need to investigate the IO subsystem.
- If an excessive amount of time is spent on 'log file sync' in comparison to the time spent on 'log file parallel write', we need to investigate the reason.
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