From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: hyrax vs. RelationBuildPartitionDesc
Date: Wed, 13 Mar 2019 13:15:45 -0400
Message-ID: <7448.1552497345@sss.pgh.pa.us> (raw)
In-Reply-To: <CA+Tgmoabw8KW9rx6ThnUTR_ofJC8GwVaC+XMe7HkZvsG7J1rvA@mail.gmail.com>
References: <CA+TgmoY3bRmGB6-DUnoVy5fJoreiBJ43rwMrQRCdPXuKt4Ykaw@mail.gmail.com>
<20190313164232.GA5270@alvherre.pgsql>
<CA+Tgmoabw8KW9rx6ThnUTR_ofJC8GwVaC+XMe7HkZvsG7J1rvA@mail.gmail.com>
Robert Haas <robertmhaas@gmail.com> writes:
> On Wed, Mar 13, 2019 at 12:42 PM Alvaro Herrera
> <alvherre@2ndquadrant.com> wrote:
>> I remember going over this code's memory allocation strategy a bit to
>> avoid the copy while not incurring potential leaks CacheMemoryContext;
>> as I recall, my idea was to use two contexts, one of which is temporary
>> and used for any potentially leaky callees, and destroyed at the end of
>> the function, and the other contains the good stuff and is reparented to
>> CacheMemoryContext at the end. So if you have any accidental leaks,
>> they don't affect a long-lived context. You have to be mindful of not
>> calling leaky code when you're using the permanent one.
> Well, that assumes that the functions which allocate the good stuff do
> not also leak, which seems a bit fragile.
I'm a bit confused as to why there's an issue here at all. The usual
plan for computed-on-demand relcache sub-structures is that we compute
a working copy that we're going to return to the caller using the
caller's context (which is presumably statement-duration at most)
and then do the equivalent of copyObject to stash a long-lived copy
into the relcache context. Is this case being done differently, and if
so why? If it's being done the same, where are we leaking?
I recall having noticed someplace where I thought the relcache partition
support was simply failing to make provisions for cleaning up a cached
structure at relcache entry drop, but I didn't have time to pursue it
right then. Let me see if I can reconstruct what I was worried about.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, robertmhaas@gmail.com, alvherre@2ndquadrant.com, pgsql-hackers@lists.postgresql.org
Subject: Re: hyrax vs. RelationBuildPartitionDesc
In-Reply-To: <7448.1552497345@sss.pgh.pa.us>
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