Re: pg_stat_activity.waiting_start

From: Stephen Frost <sfrost(at)snowman(dot)net>
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
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* 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..?



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