Wakeup LGWR if idle 2. To verify frequency of log file switching check alert log file which keep record of each log file switch. A slow LGWR process can magnify the log file sync waits, which user sessions wait on during commits or rollbacks.
The cure is the same as for the db file parallel write waits. A possible and rather common side effect is a dramatic degradation in log file sync waits which outweighs benefits from reduced latching. Then there could be some known bugs into the database.
If database redo log file size is not adequate, which cause high number log file switching. Followup September 16, - 3: Log parallelism Log parallelism is controlled by two hidden parameters: You can vent your frustration at www.
Make sure the controller that services the mount point is not overloaded. In this case, modify the application to commit at a lower frequency. The vast majority of DB time is spent on log file sync, so our results are not polluted with irrelevant waits.
Consider putting log files on striped disks. Excessive Commits from Application: Database administrator has to compare and Analyze these AWR repots.
There could be so many reasons for Log file Sync wait event, Here I would explain most obvious reasons from them. I would suggest to open a Service Request with Oracle Support for further assistance. A lower commit frequency at the expense of higher rollback segment usage can also provide some relief.
Performance troubleshooting as exact science High log file sync waits? DBA can take following steps to solve this. See Metalink Note Certain platforms and configurations carry more risk of adverse effects from log parallelism on database performance than others: The surplus time is CPU activity and is most commonly contention caused by over committing.
If a SQL statement is encountering a significant amount of total time for this event, the average wait time should be examined. The first time I run it with default log parallelism settings.I have a task which reads a large file line by line, does some logic with it, and returns a string I need to write to a file.
The order of the output does not matter. However, when I try the code below, it stops/get really slow after reading k lines of my file.
A bigger log buffer and FAR FAR FAR fewer commits (you are probably committing way way too much -- that is causing extra control file writes and log waits - the only time you want for logs; when you commit or the redo log buffer is totally full).
Oracle log file parallel writes Oracle db file sequential scattered read disk I/O speed tuning The popular Ion tool is the easiest way to analyze Oracle log file behavior over time (above plot of log file parallel writes), and Ion allows you to spot hidden redo log performance trends.
1. Slow Write on Hard Disk: One of the reason for Log file sync wait event could be slow write in to hard disk by LGWR process.
To verify this DBA has to compare AVG wait of "log file sync" and "log file parallel write" wait mi-centre.com log file parallel write is a part of log file sync wait event.
Query the V$SYSTEM_EVENT view as follows to discover the LGWR average wait time (log file parallel write event).
An average wait time of 10ms (1 centisecond) or less is generally acceptable. A higher system I/O throughput can improve the average wait time of. As the db file parallel write wait event belongs only to the DBWR process, the log file parallel write wait event belongs only to the LGWR process.
When it is time to write, the LGWR process writes the redo buffer to the online redo logs by issuing a series of system write calls to the operating system.Download