Emergency

Group commit and XA



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Returning to post Group commit and real fsync I made several experiments:

I ran sysbench update_key benchmarks without —log-bin, with —log-bin, and with —log-bin and —innodb-support-xa=0 (default value is 1). Results (in transactions / sec)

threadswithout —log-bin—log-bin—log-bin and
—innodb_support-xa=0
11218.68614.941010.44
42686.36667.771162.60
163993.59666.141161.56
643630.55665.181151.36

So we can see group commit is not only broken when XA is enabled but also if XA is disabled but binary log is enabled. Performance without XA can be twice as good as with XA if binary logs are enabled as Innodb will need to flush its log buffer only once. So, if you are using —log-bin with innodb tables it makes sense to set —innodb-support-xa=0

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