Message-ID: <2ca9a413-fe96-4c96-9781-2e85d876afd1@iki.fi>
Date: Fri, 27 Mar 2026 13:13:09 +0200
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: Memory leak in pg_stat_statements when qtext file contains
 invalid encoding
To: Daniel Gustafsson <daniel@yesql.se>
Cc: Lukas Fittl <lukas@fittl.com>, Gaurav Singh <gaurav.singh@yugabyte.com>,
 pgsql-bugs@lists.postgresql.org
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 <178e0d90-26d9-4c3a-9448-2f64f0d35dc8@iki.fi>
 <56D5EAF1-1636-45EC-97FB-3A08260417D2@yesql.se>
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From: Heikki Linnakangas <hlinnaka@iki.fi>
In-Reply-To: <56D5EAF1-1636-45EC-97FB-3A08260417D2@yesql.se>
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On 27/03/2026 11:05, Daniel Gustafsson wrote:
>> On 27 Mar 2026, at 09:59, Heikki Linnakangas <hlinnaka@iki.fi> wrote:
> 
>> Hmm, perhaps. But there's a simpler, less invasive fix. When that code was written, we didn't have MCXT_ALLOC_HUGE nor MCXT_ALLOC_NO_OOM. Now that we do, we can just use palloc_extended(MCXT_ALLOC_HUGE | MCXT_ALLOC_NO_OOM) instead of raw malloc(). Per attached.
> 
> LGTM.

Committed, thanks!


Here's one way to reproduce the invalid encoding error without 
artificially corrupting the file:

-- Run a query with a non-latin character in it. (This needs to be run 
in UTF-8 database.)
psql postgres -c 'select g as "omega Ω col" from generate_series(1, 1) g;'

-- Create a database with latin1 encoding
psql postgres -c "create database latindb encoding 'latin1' lc_ctype='C' 
lc_collate='C' template template0"

-- check pg_stat_statements() from the latin1 database
-- This fails with encoding conversion error.
PATH=~/pgsql.fsmfork/bin/ psql latindb -c "create extension 
pg_stat_statements; select * from pg_stat_statements"

If you repeat the erroring "select * from pg_stat_statements" in latindb 
many times, you can see the memory usage grow without this fix.

- Heikki