MIME-Version: 1.0
References: <CAEcQ1bYR9s4eQLFDjzzJHU8fj-MTbmRpW-9J-r2gsCn+HEsynw@mail.gmail.com>
In-Reply-To: <CAEcQ1bYR9s4eQLFDjzzJHU8fj-MTbmRpW-9J-r2gsCn+HEsynw@mail.gmail.com>
From: Lukas Fittl <lukas@fittl.com>
Date: Fri, 27 Mar 2026 01:21:39 -0700
Message-ID: <CAP53Pky1575W1euSUwj2Zc5b0kBFZqpNuvMOGCvU_bR1tmD7zA@mail.gmail.com>
Subject: Re: Memory leak in pg_stat_statements when qtext file contains
 invalid encoding
To: Gaurav Singh <gaurav.singh@yugabyte.com>
Cc: pgsql-bugs@lists.postgresql.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Archived-At: <https://www.postgresql.org/message-id/CAP53Pky1575W1euSUwj2Zc5b0kBFZqpNuvMOGCvU_bR1tmD7zA%40mail.gmail.com>
Precedence: bulk

Hi Gaurav,

On Fri, Mar 27, 2026 at 12:54=E2=80=AFAM Gaurav Singh <gaurav.singh@yugabyt=
e.com> wrote:
> If the qtext file contains an invalid encoding, pg_any_to_server calls er=
eport(ERROR) which longjmps out of the function.
> The cleanup code at the bottom of the function is never reached.
>
> LWLockRelease(pgss->lock);
> if (qbuffer)
> free(qbuffer);
> On every subsequent call, the malloc'd buffer (the entire file contents) =
is leaked, and the LWLock release is also skipped.

I don't think the analysis is correct in regards to the LWLock release
- that should be taken care of by LWLockReleaseAll on abort.

But I think you're correct about qbuffer - because that buffer is
using malloc (not palloc), its not part of any memory context, and so
it will happily leak on abort.

It appears our use of malloc in pg_stat_statements is so that we can
fail on OOM and return NULL without a jump. I think that makes sense
for when a GC cycle was triggered during regular query execution
(since we don't want to error the original query), but it seems like
just bubbling up the OOM if needed when querying the
pg_stat_statements function seems fine.

I wonder if its worth separating the two cases, since the issue you're
describing (the call to pg_any_to_server failing) only happens when
returning the query text file contents to the client. I think your
PG_FINALLY suggestion could also work, but it feels a bit tedious to
wrap the whole pg_stat_statements_internal function in it.

Thanks,
Lukas

PS: I would recommend reviewing the use of a text format email client
for posting to the Postgres mailing lists, or significantly reducing
your formatting when sending HTML emails - your email has a lot of
styling that is hard to read (even for me in Gmail), and even harder
to quote in a plain text email response.


--
Lukas Fittl