Re: [HACKERS] pg_stat_activity.waiting_start

Stephen Frost <sfrost@snowman.net> writes:
> * Tom Lane (tgl@sss.pgh.pa.us) wrote:
>> 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..?

Well, that only applies to heavyweight locks, which do a gettimeofday
anyway in order to schedule the deadlock-check timeout.  If you were
willing to populate this new column only for heavyweight locks, maybe it
could be done for minimal overhead.  But that would be backsliding
quite a lot compared to what we just did to extend pg_stat_activity's
coverage of lock types.
        regards, tom lane