From: | Stephen Frost <sfrost(at)snowman(dot)net> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Joel Jacobson <joel(at)trustly(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: pg_stat_activity.waiting_start |
Date: | 2016-12-24 02:05:40 |
Message-ID: | 20161224020539.GF18360@tamriel.snowman.net |
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Lists: | pgsql-hackers |
* Tom Lane (tgl(at)sss(dot)pgh(dot)pa(dot)us) wrote:
> Joel Jacobson <joel(at)trustly(dot)com> writes:
> > We already have xact_start, query_start and backend_start
> > to get the timestamptz for when different things happened.
>
> > I would like to propose adding a fourth such column, "waiting_start",
> > which would tell how long time a backend has been waiting.
>
> The difficulty with that is it'd require a gettimeofday() call for
> every wait start. Even on platforms where those are relatively cheap,
> the overhead would be nasty --- and on some platforms, it'd be
> astonishingly bad. We sweated quite a lot to get the overhead of
> pg_stat_activity wait monitoring down to the point where it would be
> tolerable for non-heavyweight locks, but I'm afraid this would push
> it back into the not-tolerable range.
Could we handle this like log_lock_waits..?
Thanks!
Stephen
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