From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: David Rowley <david.rowley@2ndquadrant.com>,
        Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>,
        Dmitry Dolgov <9erthalion6@gmail.com>,
        Jeff Janes <jeff.janes@gmail.com>,
        Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>,
        Pavel Stehule <pavel.stehule@gmail.com>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: why partition pruning doesn't work?
In-reply-to: 
 <CA+TgmoaQ+hxgDP4uxP_nRgC+JAn33_vona8P+GAnRDkceSZNSw@mail.gmail.com>
References: 
 <CAFj8pRBjrufA3ocDm8o4LPGNye9Y+pm1b9kCwode4X04CULG3g@mail.gmail.com>
 <CA+q6zcV5=8JoDTBNO0EUDG7++Rj_GE89MQ1sYMHLHZs5pm3V8g@mail.gmail.com>
 <CAFjFpResLp-PnVv7qBBagM-1ia6+h3pnCfDM+AJUAVWOTgHt8w@mail.gmail.com>
 <7142.1527868419@sss.pgh.pa.us>
 <CAMkU=1z3SR9jGSG7CHQaba-cq9wPTTbYcSbWPLXiLcmMtRVDYQ@mail.gmail.com>
 <1111.1527977170@sss.pgh.pa.us>
 <CA+q6zcVL=7as7ud5ZNgndH_ytUn-h1=q_v8Cqpfea4-LULweMw@mail.gmail.com>
 <10432.1528045900@sss.pgh.pa.us>
 <CA+q6zcVX9Gp0o06AXrozc0k4zkfera_wQiSyTkKXzgCsEqM6Yg@mail.gmail.com>
 <569483c5-a273-6537-1b5d-7a271ce439fb@lab.ntt.co.jp>
 <CAKJS1f9y_L-sXHwh74CGOoYcQRj8mDX9PnJqJLbpKujH1AS2ow@mail.gmail.com>
 <CAKJS1f-D1Tbi=Ozug7wfiZRf7wJs3tJ1G0cX5MK0nwstrc++tA@mail.gmail.com>
 <e6e751ea-0db4-0e7b-9513-97460edb60b3@lab.ntt.co.jp>
 <CAKJS1f_jatg5+qbrha2fGog63t3VdbNnOkYZitJtx-uo5H5EsQ@mail.gmail.com>
 <22805.1528386192@sss.pgh.pa.us>
 <CAKJS1f9xHoMntARi1RhqwAVZ-E0qp5a5f+Tf_chH9Vr8xOWiAw@mail.gmail.com>
 <21787.1528428171@sss.pgh.pa.us> <26279.1528670981@!
 sss.pgh.pa.us> <17850.1528755844@sss.pgh.pa.us>
 <CA+Tgmoa2Vvka6dBMb2w_u_N2o2HUPY6oYkS4FQ3nXMj=4Zd5ig@mail.gmail.com>
 <19365.1528820758@sss.pgh.pa.us>
 <CA+TgmoZi9hwHb4nZxCeh1TTT8rGq6AYN1Q8o5uXhiPZ3sr6o9g@mail.gmail.com>
 <30981.1528822481@sss.pgh.pa.us>
 <CA+TgmoZXtauTcAHiTdL9dRShkK+ieLgNtiuxWxYZWJpHB41iWQ@mail.gmail.com>
 <637.1528863347@sss.pgh.pa.us>
 <CA+TgmoaQ+hxgDP4uxP_nRgC+JAn33_vona8P+GAnRDkceSZNSw@mail.gmail.com>
Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Wed, 13 Jun 2018 09:47:59 -0400"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <28596.1528900759.1@sss.pgh.pa.us>
Date: Wed, 13 Jun 2018 10:39:19 -0400
Message-ID: <28597.1528900759@sss.pgh.pa.us>
Precedence: bulk

Robert Haas <robertmhaas@gmail.com> writes:
> Seems reasonable.  Really, I think we should look for a way to hang
> onto the relation at the point where it's originally opened and locked
> instead of reopening it here.  But that's probably more invasive than
> we can really justify right at the moment, and I think this is a step
> in a good direction.

The existing coding there makes me itch a bit, because there's only a
rather fragile line of reasoning justifying the assumption that there is a
pre-existing lock at all.  So I'd be in favor of what you suggest just to
get rid of the "open(NoLock)" hazard.  But I agree that it'd be rather
invasive and right now is probably not the time for it.

			regards, tom lane