Posted by peter |

I had an interesting tuning case few days ago. The system serving high traffic using Innodb tables would be stalling every so often causing even very simple queries both reads and writes taking long time to complete, with progress almost paused (dropping from thousands to tens of queries per second).

On the surface the problem looked simple – in the processlist every so often you would see a lot of queries, mostly selects taking 10+ seconds while at the same time there was no significant iowait, neither high CPU usage. Closer examination showed there were hundreds of queries stuck in the innodb queue, with innodb_thread_concurrency set to 8
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