From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Curing plpgsql's memory leaks for statement-lifespan values |
Date: | 2016-07-25 18:50:48 |
Message-ID: | 5916.1469472648@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Attached is a draft patch for creating statement-level temporary memory
contexts in plpgsql. It creates such contexts only as needed, and there
are a lot of simpler plpgsql statements that don't need them, so I think
the performance impact should be pretty minimal --- though I've not tried
to measure it, since I don't have a credible benchmark for overall plpgsql
performance.
This fixes the originally complained-of leak and several others besides,
including at least one path that leaked function-lifespan memory even
without an error :-(.
In addition to the patch proper, I attach for amusement's sake some
additional hacking I did for testing purposes, to make sure I'd found and
accounted for all the places that were allocating memory in the SPI Proc
context. There's a glibc-dependent hack in aset.c that reports any
plpgsql-driven palloc or pfree against a context named "SPI Proc", as
well as changes in pl_comp.c so that transient junk created during initial
parsing of a plpgsql function body doesn't end up in the SPI Proc context.
(I did that just to cut the amount of noise I had to chase down. I suppose
in large functions it might be worth adopting such a change so that that
junk can be released immediately after parsing; but I suspect for most
functions it'd just be an extra context without much gain.)
Although this is in principle a bug fix, it's invasive enough that I'd
be pretty hesitant to back-patch it, or even to stick it into HEAD
post-beta. I'm inclined to sign it up for the next commitfest instead.
regards, tom lane
Attachment | Content-Type | Size |
---|---|---|
plpgsql-stmt-mcontext-1.patch | text/x-diff | 68.7 KB |
plpgsql-alloc-test.patch | text/x-diff | 5.6 KB |
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