Adaptive Log File Sync in Oracle 11gR2

DB: Oracle 11.2.0.4.8 RAC
OS: Solaris SPARC 64bit
Storage: IBM DS8800

Frequent switching between post/wait and polling was observed. Maximum ‘log file sync’ could be up to 120 ms while average wait time for ‘log file parallel write’ is approximately 13 ms. Orion summary indicates the minimum I/O latency is about 5-6 ms.

Although this issue has not been confirmed, we believe that the long ‘log file sync’ was caused by Adaptive Log File Sync, which was enabled since 11.2.0.3.

Reference:

Adaptive Log File Sync Optimization (Doc ID 1541136.1)
SPARC: Reducing High Waits on ‘log file sync’ on Oracle Solaris SPARC by Increasing Priority of Log Writer (Doc ID 1523164.1)
High Waits for ‘Log File Sync’: Known Issue Checklist for 11.2 (Doc ID 1548261.1)
Bug 14823372 – Adaptive “log file sync” picks inaccurate polling interval on RAC (Doc ID 14823372.8)
Bug 13074706 – Long “log file sync” waits in RAC not correlated with slow writes (Doc ID 13074706.8)
Bug 13707904 – LGWR sometimes uses polling, sometimes post/wait (Doc ID 13707904.8)
Adaptive Switching Between Log Write Methods can Cause ‘log file sync’ Waits (Doc ID 1462942.1)

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