The parameter _use_adaptive_log_file_sync was introduced in 11gR2 and controls whether adaptive switching between post/wait and polling is enabled.
DEFAULT VALUE of this parameter is TRUE. i.e according to oracle algorithm and internal statistics, the adaptive switching will happen between post/wait and polling method.

There are 2 methods by which LGWR and foreground processes can communicate in order to acknowledge that a commit has completed:
Post/wait: traditional method available in previous Oracle releases LGWR explicitly posts all processes waiting for the commit to complete.

Polling: Foreground processes sleep and poll to see if the commit is complete.

Below is the snippet from lgwr trace, which shows adaptive switching between these methods.

However, there are few cases, where this adaptive switching caused the lgwr process to block other session or causes huge log file sync waits.
In that case, if you wish to disable this feature, then

NOTE – Please check with oracle support before doing this change in the production database.


You can check the redo polling stats from the database using below query.