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Answer: The log file sync wait occurs at the end of a transaction (COMMIT or EOJ)and the database writer (DBWR) process must wait for the log file to synchronize with the database. Oracle guru Steve Adams notes details on how Oracle processes log file sync waits:
Total time wait for Log file sync is 868,667 and out of it 93,144 times it was waiting for log file parallel write wait event which is quite high. One more important criteria to major I/O is If an average time for 'log file parallel write' is over 20 milliseconds this means problem with IO subsystem.
session 12 asks LGWR to do something, and then waits on log file sync. But they are waiting on *another* session (lgwr) to do its work. LGWR will then have the 'log file parallel write' waits for its session. For normal read: session 12 *does* the I/O, hence its waits (db file seq… etc) *are* the I/O cost (as perceived by Oracle).
Nov 10, 2011 · In 11gr1 we are seeing the logfile sync wait event in top event of awr report. We have optimized the storage still we are finding the same. Nature of Application as every commit after one transaction complete.
The user session will post the LGWR to write all redo required from the log buffer to the redo log file. When the LGWR has finished it will post the user session. The user session waits on this wait event while waiting for LGWR to post it back to confirm all redo changes are safely on disk.
Oracle does not really wait on this event; the foreground only yields the CPU. Thus, the chances of catching this event are very low. This is not an application induced deadlock, but an assumed deadlock by the cache layer. The cache layer cannot get a buffer in a certain mode within a certain amount of time. … log file sync. When a user …
Jun 17, 2014 · Oracle Log File Sync Wait Event The Oracle "log file sync" wait event is triggered when a user session issues a commit (or a rollback). The user session will signal or 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.Author: Facedba
The Oracle “log file sync” wait event is triggered when a user session issues a commit (or a rollback). The user session will signal or post the LGWR to write the log buffer to the redo log file. The user session will signal or post the LGWR to write the log buffer to the redo log file.
Jul 07, 2008 · In a nutshell, after posting LGWR to write, user or background processes waits for LGWR to signal back with 1 sec timeout. User process charges this wait time as ‘log file sync’ event. In the prior section, ‘log file sync’ waits starts at step 2 after semctl call and completes after step 5 above. Root causes of ‘log file sync’ waits