On Sun, Nov 24, 2019 at 8:52 AM Mariel Cherkassky <mariel.cherkassky@xxxxxxxxx> wrote:
Hey Andrew,It seems that changing this parameter worked for me.Setting it to zero means that there wont be any parallel workers for one query right ?Is it something familiar this problem with the gatherers ?
Your example would not be using parallel workers anyway, regardless of the setting of max_parallel_workers_per_gather, so I don't see how changing this could have worked for you. Unless you mean it worked in your full test, rather than in your test case. I doubt your test case benchmarking was very reliable to start with, you only show a single execution and didn't indicate you had more unshown ones.
If I do more credible benchmarking, I do get a performance regression but it closer is to 16% than to 3 fold. And it doesn't depend on the setting of max_parallel_workers_per_gather. I doubt a regression of this size is even worth investigating.
pgbench -T300 -P5 -f <(echo "select count(*) from test1") -p 9912 -n -M prepared
Cheers,
Jeff
