Re: Why are we waiting?

Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> On Wed, 2008-02-06 at 14:42 -0500, Tom Lane wrote:
>> Not really, considering the extremely limited use of LW_SHARED in lock.c
>> (GetLockConflicts is used only by CREATE INDEX CONCURRENTLY, and
>> GetLockStatusData only by the pg_locks view). For the type of benchmark
>> that I gather this is, there should be *zero* LW_SHARED acquisitions at
>> all. And even if there are some, they could only be blocking against
>> the (undoubtedly much more frequent) LW_EXCLUSIVE acquisitions; it's not
>> very credible that there is zero contention among the LW_EXCLUSIVE locks
>> yet a few shared acquirers manage to get burnt.

> ...but the total wait time on those lock waits was 24 microseconds. I
> hardly call that burnt.

What you are failing to grasp is that the data is simply not credible
(unless perhaps Staale fesses up that his benchmark includes a whole lot
of pg_locks monitoring, in which case I'd want to see it redone without
anyway).

regards, tom lane