Re: LWlock:LockManager waits

you mean too many concurrent sessions trying to acquire lock on same
relation , then waiting on "LockManager" LWlock,right? this contention
occurred on parsing ,planning, or execute step ?

Thanks,

James

Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> 於 2024年4月9日週二 下午12:31寫道：

> On Tue, 2024-04-09 at 11:07 +0800, James Pang wrote:
> > we found sometimes , with many sessions running same query "select
> ..." at the same time, saw many sessions waiting on "LockManager". for
> example, pg_stat_activity show. It's a production server, so no enable
> trace_lwlocks flag. could you direct me what's the possible reason and how
> to reduce this "lockmanager" lock? all the sql statement are "select " ,no
> DML.
> >
> > time wait_event
> count(pid)
> > 2024-04-08 09:00:06.043996+00 | DataFileRead | 42
> > 2024-04-08 09:00:06.043996+00 | | 15
> > 2024-04-08 09:00:06.043996+00 | LockManager | 31
> > 2024-04-08 09:00:06.043996+00 | BufferMapping | 46
> > 2024-04-08 09:00:07.114015+00 | LockManager | 43
> > 2024-04-08 09:00:07.114015+00 | DataFileRead | 28
> > 2024-04-08 09:00:07.114015+00 | ClientRead | 11
> > 2024-04-08 09:00:07.114015+00 | | 11
>
> That's quite obvious: too many connections cause internal contention in
> the database.
>
> Reduce the number of connections by using a reasonably sized connection
> pool.
>
> Yours,
> Laurenz Albe
>