log file sync
When a user session commits, the session's redo information must be flushed to the redo logfile.
Detailed Description​
When a user session commits, the session's redo information must be flushed to the redo logfile. The user session will post the LGWR to write the log buffer to the redo log file. When the LGWR has finished writing, it will post the user session.
In order to ensure database integrity, when you issue a commit statement, your session's changes must be saved to disk. Oracle writes these changes to transaction logs called 'redo logs' which allow the database to be rolled forward in case of recovery. It is the job of the Log Writer process (LGWR) to write these changes to disk. log file sync waits are seen whilst these writes are taking place.
How to reduce this wait​
If this event's waits constitute a significant wait on the system or a significant amount of time waited by a user experiencing response time issues or on a system, then examine the average time waited.
If the average time waited is low, but the number of waits are high, then the application might be committing after every INSERT, rather than batching COMMITs. Applications can reduce the wait by committing after 50 rows, rather than every row.
If the average time waited is high, refer to the Oracle Tuning Guide for further information on tuning the redo logs.
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