Re: pg_dump issues

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Cc: Andrew Dunstan <andrew(at)dunslane(dot)net>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pg_dump issues
Date: 2011-10-03 16:02:14
Message-ID: 16626.1317657734@sss.pgh.pa.us
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Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> Excerpts from Tom Lane's message of lun oct 03 01:47:18 -0300 2011:
>> (Without cassert, it looks like LockReassignCurrentOwner is the next
>> biggest time sink; I'm wondering if there's some sort of O(N^2) behavior
>> in there.)

> That seems fishy. Even if there weren't quadratic behavior, should this
> be called at all? AFAIK it should only be used on cases where there are
> subtransactions at work, and I don't think pg_dump uses them.

I wondered that too, but the calls are legit --- they're coming from
PortalDrop.

It appears that most of the calls don't actually have anything to do,
but they're iterating through a rather large local lock table to find
that out. We probably ought to think of a way to avoid that. The trick
is to not make performance worse for typical small transactions that
aren't holding many locks (which I think was the design center for this
to begin with).

regards, tom lane

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