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db file parallel write

Article by Rampant Author Brian Carr

The db file parallel write wait event occurs when the process, typically DBWR, has issued multiple I/O requests in parallel to write dirty blocks from the buffer cache to disk, and is waiting for all requests to complete. If this is a significant portion of the total wait time it is not necessarily having a large impact on on user sessions. However this combined with the waits from free buffer waits shows that this is impacting user sessions. this

Recommendation: Be sure async I/O is enabled for the platform, because you want to be absolutely sure that the maximum possible bandwidth is available to DBWR, also make sure the disk layout allows the most amount of performance to the disks RAID 1+0). Consideration should be given to converting to RAW for better performance along with turning on ASYNC I/O. Also ensure there is enough buffer cache to prevent thrashing going on with the buffer cache.





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