From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: hyrax vs. RelationBuildPartitionDesc |
Date: | 2019-03-13 17:15:45 |
Message-ID: | 7448.1552497345@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Wed, Mar 13, 2019 at 12:42 PM Alvaro Herrera
> <alvherre(at)2ndquadrant(dot)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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