On Mon, Jul 22, 2019 at 2:42 AM Fabio Pardi <f.pardi@xxxxxxxxxxxx> wrote:
Hello,
I recently spent a bit of time benchmarking effective_io_concurrency on Postgres.
I would like to share my findings with you:
https://portavita.github.io/2019-07-19-PostgreSQL_effective_io_concurrency_benchmarked/
Comments are welcome.
regards,
fabio pardi
You didn't mention what type of disk storage you are using, or if that matters. The number of cores in your database could also matter.
Does the max_parallel_workers setting have any influence on how effective_io_concurrency works?
Based on your data, one should set effective_io_concurrency at the highest possible setting with no ill effects with the possible exception that your disk will get busier. Somehow I suspect that as you scale the number of concurrent disk i/o tasks, other things may start to suffer. For example does CPU wait time start to increase as more and more threads are consumed waiting for i/o instead of doing other processing? Do you run into lock contention on the i/o subsystem? (Back in the day, lock contention for /dev/tcp was a major bottleneck for scaling busy webservers vertically. I have no idea if modern linux kernels could run into the same issue waiting for locks for /dev/sd0. Surely if anything was going to push that issue, it would be setting effective_io_concurrency really high and then demanding a lot of concurrent disk accesses.)
