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Re: [PERFORM] No hash join across partitioned tables?

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: [PERFORM] No hash join across partitioned tables?
Date: 2010-06-14 03:47:06
Message-ID: AANLkTimMPlDh1mkH2ZzXTQF_GvlIq1Op78AaiP285F8Q@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-performance
On Thu, Jun 10, 2010 at 9:29 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> (moving to -hackers)
>
> On Wed, Jun 9, 2010 at 4:11 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Robert Haas <robertmhaas(at)gmail(dot)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.
>
> I guess I can't really disagree with that.  Should we try to document
> this in some way?

Proposed patch attached.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company

Attachment: analyze-inherit-docs.patch
Description: application/octet-stream (1.0 KB)

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