From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: why partition pruning doesn't work? |
Date: | 2018-07-16 00:12:37 |
Message-ID: | CA+TgmoZcHQK+sD5yJrWU6vnZ_x5RaYyLtNP_tUUcrUhRorz=9A@mail.gmail.com |
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On Sun, Jul 15, 2018 at 1:02 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> What we'd be better off doing, if we go this route, is to install an
> assertion-build-only test that verifies during relation_open(NoLock)
> that some kind of lock is already held on the rel. That would protect
> not only the executor, but a boatload of existing places that open
> rels with NoLock on the currently-unverified assumption that a lock is
> already held.
+1. In fact, maybe we ought to go a little further and have a
relation_reopen(oid, mode) that verifies that a lock in the specified
mode is held.
And then maybe we ought to go even further and start trying to get rid
of all the places where we reopen already-opened relations. A
distressing number of new patches add more places that do that, and
while I try to push back on those, I think they are proliferating, and
I think that they are not free. Granted, a hash table lookup is
pretty cheap, but if you do a sufficient number of them in
commonlt-taken code paths, it's got to cost something.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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