To: Stephen Frost <sfrost@snowman.net>
cc: Tatsuo Ishii <ishii@postgresql.org>, pgsql-performance@postgresql.org,
	pgsql-hackers@postgresql.org
Subject: Re: pg_dump and thousands of schemas 
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>
Comments: In-reply-to Stephen Frost <sfrost@snowman.net>
	message dated "Thu, 31 May 2012 00:01:49 -0400"
Date: Thu, 31 May 2012 00:18:17 -0400
Message-ID: <26886.1338437897@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

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