Feedback-ID: i0fe9450f:Fastmail
Date: Mon, 2 Mar 2026 09:20:37 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Chao Li <li.evan.chao@gmail.com>
Cc: Corey Huinker <corey.huinker@gmail.com>,
	Postgres hackers <pgsql-hackers@lists.postgresql.org>,
	Tomas Vondra <tomas@vondra.me>
Subject: Re: Defects with invalid stats data for expressions in extended stats
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On Mon, Mar 02, 2026 at 07:39:45AM +0800, Chao Li wrote:
> But why do we still explicitly free the stats array? My concern is
> mostly about =E2=80=9Cpartial free=E2=80=9D: either free everything, or f=
ree nothing
> and let the memory context clean it up. =E2=80=9CPartial free=E2=80=9D te=
nds to
> confuse code readers, and future readers may keep running into the
> same question.=20

Not necessarity.  We have plenty of these patterns in the code with
such partial frees.  At the end, two things tend to take priority:
the readability of the code as well as its efficiency because repeated
pfree() calls can be more expensive than a memory context cleanup,
particularly in hot loops, though doing pfree() calls may be better in
some cases.

In this case, I see a better argument with the code clarity, as we use
the same array for the stats built with attributes and expressions.
We also cap the number of expressions to 8, which puts some control.
But at the end it does not really matter: in this context ANALYZE
makes sure that nothing crosses the processing of a single relation,
even with a transaction analyzes a lot of relations (same or
different).
--
Michael

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