From: Tom Lane <tgl@sss.pgh.pa.us>
To: Stephen Frost <sfrost@snowman.net>
Cc: Tatsuo Ishii <ishii@postgresql.org>
Cc: pgsql-performance@postgresql.org
Cc: pgsql-hackers@postgresql.org
Subject: Re: pg_dump and thousands of schemas
Date: Thu, 31 May 2012 00:18:17 -0400
Message-ID: <26886.1338437897@sss.pgh.pa.us> (raw)
In-Reply-To: <20120531040149.GC1267@tamriel.snowman.net>
References: <20120529.185149.1127748531209576379.t-ishii@sraoss.co.jp>
<12147.1338306742@sss.pgh.pa.us>
<20120530.180620.600165924826262795.t-ishii@sraoss.co.jp>
<20120531.092043.1953698679173443322.t-ishii@sraoss.co.jp>
<26386.1338436470@sss.pgh.pa.us>
<20120531040149.GC1267@tamriel.snowman.net>
Stephen Frost <sfrost@snowman.net> writes:
> The current situation where the client-to-server latency accounts for
> multiple minutes of time is just ridiculous, however, so I feel we need
> some form of this patch, even if the server side is magically made much
> faster. The constant back-and-forth isn't cheap.
No, you're missing my point. I don't believe that client-to-server
latency, or any other O(N) cost, has anything to do with the problem
here. The problem, as Jeff has demonstrated, is the O(N^2) costs
associated with management of the local lock table. It is utterly
pointless to worry about O(N) costs until that's fixed; and it's just
wrong to claim that you've created a significant speedup by eliminating
a constant factor when all you've done is staved off occurrences of the
O(N^2) problem.
Once we've gotten rid of the local lock table problem, we can re-measure
and see what the true benefit of this patch is. I'm of the opinion
that it will be in the noise compared to the overall runtime of pg_dump.
I could be wrong, but you won't convince me of that with measurements
taken while the local lock table problem is still there.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, sfrost@snowman.net, ishii@postgresql.org, pgsql-hackers@postgresql.org
Subject: Re: pg_dump and thousands of schemas
In-Reply-To: <26886.1338437897@sss.pgh.pa.us>
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