| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Gregory Stark <stark(at)enterprisedb(dot)com>, Staale Smedseng <Staale(dot)Smedseng(at)Sun(dot)COM>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Why are we waiting? |
| Date: | 2008-02-06 19:49:34 |
| Message-ID: | 1202327374.29242.145.camel@ebony.site |
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| Lists: | pgsql-hackers |
On Wed, 2008-02-06 at 14:42 -0500, Tom Lane wrote:
> Simon Riggs <simon(at)2ndquadrant(dot)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
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