Bogus duplicate-message complaints from PG mail lists - Mailing list pgsql-www

Several times over the past couple of days, I have gotten complaints
like the one attached about duplicate message IDs.  I can see from my
sendmail daemon's log that I sent only one copy of this, and the
complaint is dated about twenty minutes after the fact, so I'm pretty
sure the duplicate is not of my making.

Usually when I get this type of thing I can tell from the Received:
lines that it's the fault of some list subscriber's MUA re-submitting
a message to the lists.  But the Received: lines in this example and
the last couple don't show that the message has gone anywhere outside
postgresql.org.  So I'm thinking it's a recently-introduced glitch in
the mail list server arrangements.

            regards, tom lane

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Date: Tue, 15 Jan 2013 20:31:03 +0000
From: pgsql-hackers-owner@postgresql.org
To: Tom Lane <tgl@sss.pgh.pa.us>
Subject: Denied post to pgsql-hackers
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Your message to the pgsql-hackers list has been denied
for the following reason(s):

A message was previous posted with this Message-ID
Duplicate Message-ID - <1723.1358280662@sss.pgh.pa.us> (Tue Jan 15 20:11:10 2013)
Duplicate Message Checksum (Tue Jan 15 20:11:10 2013)
Duplicate Partial Message Checksum (Tue Jan 15 20:11:10 2013)


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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Bruce Momjian <bruce@momjian.us>
cc: Robert Haas <robertmhaas@gmail.com>, Simon Riggs <simon@2ndquadrant.com>,
        Jeff Janes <jeff.janes@gmail.com>,
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Subject: Re: [HACKERS] [PERFORM] Slow query: bitmap scan troubles
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<20130115194639.GG27934@momjian.us>
Comments: In-reply-to Bruce Momjian <bruce@momjian.us>
    message dated "Tue, 15 Jan 2013 14:46:39 -0500"
Date: Tue, 15 Jan 2013 15:11:02 -0500
Message-ID: <1723.1358280662@sss.pgh.pa.us>
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Bruce Momjian <bruce@momjian.us> writes:
> On Mon, Jan 14, 2013 at 12:56:37PM -0500, Tom Lane wrote:
>> Remember also that "enable_seqscan=off" merely adds 1e10 to the
>> estimated cost of seqscans.  For sufficiently large tables this is not
>> exactly a hard disable, just a thumb on the scales.  But I don't know
>> what your definition of "extremely large indexes" is.

> Wow, do we need to bump up that value based on larger modern hardware?

I'm disinclined to bump it up very much.  If it's more than about 1e16,
ordinary cost contributions would disappear into float8 roundoff error,
causing the planner to be making choices that are utterly random except
for minimizing the number of seqscans.  Even at 1e14 or so you'd be
losing a lot of finer-grain distinctions.  What we want is for the
behavior to be "minimize the number of seqscans but plan normally
otherwise", so those other cost contributions are still important.

Anyway, at this point we're merely speculating about what's behind
Robert's report --- I'd want to see some concrete real-world examples
before changing anything.

            regards, tom lane


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