Oracle log file sync wait

What is the Best File Sync program? As per my understanding, Log - File - Sync wait is the duration, after which I receive an acknowledgement that my commit is successful. In my database the only prominent issue I see is huge log - file - sync waits.

There are cpu and each one is core. To verify this DBA has to compare AVG wait of log file sync and log file parallel write wait event.

Since log file parallel write is a part of log file sync wait event. How do I tune to reduce the log file sync wait events? Log file sync wait event: other considerations. When a user session COMMITs (or rolls back), the sessions redo information needs to be flushed to the redo log file. 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. Does that mean that 101k log file sync event waits are caused by one and only commits. On the contrary AWR also says commits per minute.

You have queried differently to get user commits. Wait Time: The wait time includes the writing of the log buffer and the post. High commit frequency is the number one cause for foreground log file sync waits. Hi Riyaj, I am currently investigating performance problem of an APPS database. The overall wait time for log file sync can be broken down into several components.

Which means that the response time of the commit is nearly immediate (only the time to update the transaction table). But of course, we may lose a commited transaction if log writer didn’t have time to write it before an instance crash. The time between the user session posting the LGWR and the LGWR posting the user after the write has completed is the wait time for ‘ log file sync ’ that the user session will show. This occurs when a user commits a transaction (a transaction is not considered committed until all of the redo to recover the transaction has been successfully written to disk).

The log file sync Oracle metric indicates the process is waiting for LGWR to finish flushing the log buffer to disk. Oracle Database - Enterprise Edition - Version 11. This wait event is triggered when an operation such as a direct path load compares the current SCN against the last on-disk commit SCN.

And the top wait event is log file sync. I have performance issue with Oracle instance. I tried to change some Oracle datab. More commits, more “ log file sync ” wait event and eventually poisonous for the scalability of your system.

Check the alert file to make sure that archiving has not stopped due to a failed archive write.

When determining the source of log file sync waits, it is important to look at another redo-related event, log file parallel write. Typically this is caused by slow writes or committing too frequently in the application. Checking the user commits section in the AWR report can reveal if the issue is related to frequent committing.

If the server is very busy, LGWR can starve for CPU too. This will lead to slower response from LGWR, increasing ‘ log file sync ’ waits. In this case, ‘ log file sync ’ is a secondary symptom and resolving the root cause for high CPU usage will reduce ‘ log file sync ’ waits.

In Oracle 9i the size of LOG _BUFFER (as recommended by SAP) was around 1MB. If your system still shows high log file sync wait times after ensuring the general tuning tips above are complete you should break down the total wait time into the individual components, then tune those components that make up the largest time.