Re: Why are we waiting?

On Wed, 2008-02-06 at 14:42 -0500, Tom Lane wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
> > There were only 2 lock delays for FirstLockMgrLock in SHARED mode, so it
> > seems believable that there were 0 lock delays in EXCLUSIVE mode.
> 
> 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.

--  Simon Riggs 2ndQuadrant  http://www.2ndQuadrant.com