|From:||Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>|
|To:||Stephen Frost <sfrost(at)snowman(dot)net>|
|Cc:||Joel Jacobson <joel(at)trustly(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>|
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Stephen Frost <sfrost(at)snowman(dot)net> writes:
> * Tom Lane (tgl(at)sss(dot)pgh(dot)pa(dot)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
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