To: Robert Haas <robertmhaas@gmail.com>
cc: Bruce Momjian <bruce@momjian.us>, Kris Jurka <books@ejurka.com>,
	pgsql-performance@postgresql.org
Subject: Re: No hash join across partitioned tables? 
In-reply-to: <AANLkTinx8lLTEKWcyEQ1rxVz6WMJVKNezfXW5TKnNAU6@mail.gmail.com> 
References: <201002252346.o1PNkXG07892@momjian.us>
	<9477.1267142614@sss.pgh.pa.us>
	<603c8f071003020816j77b3ec63wbad0415df003c0f1@mail.gmail.com>
	<17546.1267546998@sss.pgh.pa.us>
	<AANLkTinx8lLTEKWcyEQ1rxVz6WMJVKNezfXW5TKnNAU6@mail.gmail.com>
Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Wed, 09 Jun 2010 15:47:55 -0400"
Date: Wed, 09 Jun 2010 16:11:25 -0400
Message-ID: <489.1276114285@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Robert Haas <robertmhaas@gmail.com> writes:
> In going back through emails I had marked as possibly needing another
> look before 9.0 is released, I came across this issue again.  As I
> understand it, analyze (or analyse) now collects statistics for both
> the parent individually, and for the parent and its children together.
>  However, as I further understand it, autovacuum won't actually fire
> off an analyze unless there's enough activity on the parent table
> considered individually to warrant it.  So if you have an empty parent
> and a bunch of children with data in it, your stats will still stink,
> unless you analyze by hand.

Check.

> Assuming my understanding of the problem is correct, we could:

> (a) fix it,
> (b) document that you should consider periodic manual analyze commands
> in this situation, or
> (c) do nothing.

> Thoughts?

The objections to (a) are that it might result in excessive ANALYZE work
if not done intelligently, and that we haven't got a patch ready anyway.
I would have liked to get to this for 9.0 but I feel it's a bit late
now.

			regards, tom lane