Subject: Re: speeding up planning with partitions
References: <9d7c5112-cb99-6a47-d3be-cf1ee6862a1d@lab.ntt.co.jp>
 <CAH2-WznUbJx8OKohHcetyWQRy4LXEfbpTcAGFvc5K6i1BSG40w@mail.gmail.com>
From: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
Message-ID: <44463425-9eb0-3cef-eef2-0fbdb97c71dc@lab.ntt.co.jp>
Date: Tue, 11 Sep 2018 10:42:15 +0900
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To: Peter Geoghegan <pg@bowt.ie>
Cc: Pg Hackers <pgsql-hackers@postgresql.org>,
        Pavan Deolasee <pavan.deolasee@2ndquadrant.com>,
        Simon Riggs <simon@2ndquadrant.com>
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On 2018/09/11 10:11, Peter Geoghegan wrote:
> On Wed, Aug 29, 2018 at 5:06 AM, Amit Langote
> <Langote_Amit_f8@lab.ntt.co.jp> wrote:
>> It is more or less well known that the planner doesn't perform well with
>> more than a few hundred partitions even when only a handful of partitions
>> are ultimately included in the plan.  Situation has improved a bit in PG
>> 11 where we replaced the older method of pruning partitions one-by-one
>> using constraint exclusion with a much faster method that finds relevant
>> partitions by using partitioning metadata.  However, we could only use it
>> for SELECT queries, because UPDATE/DELETE are handled by a completely
>> different code path, whose structure doesn't allow it to call the new
>> pruning module's functionality.  Actually, not being able to use the new
>> pruning is not the only problem for UPDATE/DELETE, more on which further
>> below.
> 
> This was a big problem for the SQL MERGE patch. I hope that this
> problem can be fixed.

Sorry if I've missed some prior discussion about this, but could you
clarify which aspect of UPDATE/DELETE planning got in the way of SQL MERGE
patch?  It'd be great if you can point to an email or portion of the SQL
MERGE discussion thread where this aspect was discussed.

In the updated patch that I'm still hacking on (also need to look at
David's comments earlier today before posting it), I have managed to
eliminate the separation of code paths handling SELECT vs UPDATE/DELETE on
inheritance tables, but I can't be sure if the new approach (also) solves
any problems that were faced during SQL MERGE development.

Thanks,
Amit