Re: list_free() in index_get_partition()

From: Michael Paquier <michael(at)paquier(dot)xyz>
To: Justin Pryzby <pryzby(at)telsasoft(dot)com>
Cc: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: list_free() in index_get_partition()
Date: 2020-11-06 00:32:35
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On Thu, Nov 05, 2020 at 02:36:06PM -0600, Justin Pryzby wrote:
> Seems to be missing.

Any code paths calling index_get_partition() is in tablecmds.c,
involving commands that are not that hot with such lookups, but that
could be an issue if this gets called by some out-of-core code if
memory context cleanup is sloppy. So I agree to fix this one and
backpatch down to 12. I'd like to apply your fix, except if Alvaro
thinks differently as that's his commit originally. So let's wait a
bit first.

> The 2nd patch does some more cleanup - Before, a failed syscache lookup would
> ERROR, but I don't think that's supposed to happen. get_rel_relispartition()
> would instead return false, and we won't call get_partition_parent().

The cache lookup error is here as a safeguard to remind that any code
path calling index_get_partition() needs a proper lock on the
relations involved before doing such lookups, so that's a defensive
move. By switching the code as you do in 0002, you could mask such
logical problems as different errors could get raised. So I don't
think that it is a good idea.

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