In this post I’m sharing my recent experience troubleshooting a rather complex performance issue. The issue showed up during performance testing of a new platform (Exadata Cloud at Customer or ExaCC) where an application is migrating from the current one (on-premises Exadata).
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Last year, I spent some time researching redo log related performance problems, which resulted in a mini-series, including one post devoted specifically to one previously unknown scenario of excessive log file sync waits. I am happy to announce that a service request opened on the back of this research resulted in the MOS note on “log file parallel write” wait event (Doc ID 34583.1) having been updated with a general description of this scenario and factors that may contribute to it. Unfortunately, more specific information regarding this issue has been put to an internal Oracle note because of the limitations that concern underscore parameters. So if you are dealing with log file sync (or log buffer space) issues, then I strongly recommend to log in to MOS and familiarize yourself with the updated version of the note as soon as possible.
Log buffer space is a simple, yet frequently misunderstood wait event. The main reason for that is probably its name. It sounds as if it points immediately to the answer: if space in the log buffer is the issue, then increasing it surely should resolve it. Well, unfortunately even though log buffer space is simple, it’s not that simple.
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