On Mon, Feb 12, 2024 at 5:31 AM jian he <jian.universal...@gmail.com> wrote: > > On Wed, Feb 7, 2024 at 12:58 PM Ashutosh Bapat > <ashutosh.bapat....@gmail.com> wrote: > > > > > > > > > */ > > > > How bad this performance could be. Let's assume that a query is taking > > > > time and pg_log_query_plan() is invoked to examine the plan of this > > > > query. Is it possible that the looping over all the locks itself takes > > > > a lot of time delaying the query execution further? > > > > corner case test: > pgbench --initialize --partition-method=range --partitions=20000 > Somehow my setup, the pg_bench didn't populate the data but there are > 20000 partitions there. > (all my other settings are default) > > some interesting things happened when a query touch so many partitions like: > select abalance, aid from public.pgbench_accounts,pg_sleep(4) where aid > 1; > > in another session, if you immediate call SELECT pg_log_query_plan(9482); > then output be > ` > LOG: backend with PID 9482 is not running a query or a subtransaction > is aborted > ` > however if you delay a little bit of time (like 1 second), then > LOG will emit the plan with lots of text (not sure the plan is right). > > I think the reason is that the `InitPlan` within > standard_ExecutorStart takes more time to finish > when your query touches a lot of partitions.
That's probably expected unless we make the ActiveQueryDesc available before ExecutorRun. How much time did it took between issuing SELECT pg_log_query_plan(9482); and plan getting output to the server error logs? How does this time compare with say the same time difference for a simple query and how much of that time can be attributed to Lock table hash scan, if the difference between time difference is huge. -- Best Wishes, Ashutosh Bapat