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Subject: Re: pgsql: Add function to get memory context stats for processes
From: Daniel Gustafsson <dgustafsson@postgresql.org>
In-Reply-To: <CA+TgmoZgOwiF1auY+wxUBC+7GcjKqXFBf7D97sF4WL7HER4LgA@mail.gmail.com>
Date: Tue, 22 Apr 2025 10:11:43 +0200
Cc: Andres Freund <andres@anarazel.de>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
 Rahila Syed <rahilasyed90@gmail.com>
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To: Robert Haas <robertmhaas@gmail.com>
Archived-At: <https://www.postgresql.org/message-id/8EBFBFBC-DAC2-4521-AE16-069F7FD8EFBC%40postgresql.org>
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> On 17 Apr 2025, at 16:42, Robert Haas <robertmhaas@gmail.com> wrote:
>=20
> On Tue, Apr 15, 2025 at 6:11=E2=80=AFAM Andres Freund =
<andres@anarazel.de> wrote:
>> There very well could be a CFI - but it better be somewhere where the
>> in-memory state is consistent. Otherwise an error inside raised in =
the CFI
>> would lead the in-memory state inconsistent which then would cause =
problems
>> when cleaning up the dsa during resowner release or process exit.
>>=20
>> What am I missing here?
>=20
> I think maybe you're only thinking about gathering the data. What
> about publishing it? If the DSA code were interrupted at a CFI and the
> interrupting code went and tried to perform a DSA allocation to store
> the resulting data and then returned to the interrupted DSA operation,
> would you expect the code to cope with that? I do not believe we have
> anywhere enough guarantees about reentrancy for that to be safe.

Do you mean that an interrupt handler will make DSA allocations?  I =
don't think
that would be something we'd want to allow regardless of this patch.  Or =
did I
misunderstand the above?

--
Daniel Gustafsson