[BUG] temporary file usage report with extended protocol and unnamed portals

From: Frédéric Yhuel <frederic(dot)yhuel(at)dalibo(dot)com>
To: PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Cc: Benoit Lobréau <benoit(dot)lobreau(at)dalibo(dot)com>, Guillaume Lelarge <guillaume(dot)lelarge(at)dalibo(dot)com>, Pierrick Chovelon <pierrick(dot)chovelon(at)dalibo(dot)com>
Subject: [BUG] temporary file usage report with extended protocol and unnamed portals
Date: 2025-04-18 08:49:58
Message-ID: 3d07ee43-8855-42db-97e0-bad5db82d972@dalibo.com
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Hi,

It seems there's a bug in the logging of temporary file usage when the
extended protocol is used with unnamed portals.

For example, with the attached Java / pgJDBC programs, we get the
following logs:

[...] LOG: temporary file: path "base/pgsql_tmp/pgsql_tmp525566.0",
size 2416640
[..] STATEMENT: SELECT 1

but it should be:

[...] LOG: temporary file: path "base/pgsql_tmp/pgsql_tmp538230.0",
size 2416640
[...] STATEMENT: SELECT * FROM foo ORDER BY a OFFSET $1 LIMIT 2

It has been tested with HEAD and REL_17_STABLE.

My guess is that there's a race somewhere, probably when the global
variable "debug_query_string" is set.
The unnamed portal is closed when the BIND of the next query arrives
(here: SELECT 1), and I suspect that the variable is set before the
temporary file is deleted (and logged).

pgJDBC uses unnamed portals, but I don't think this is specific to JDBC.
I see the same problem with the attached Python / psycopg3 program.
I think it would be better if the drivers used named portals all the
time (and an explicit close message), but this seems to be a postgres bug.

What do you think?

Best regards,
Frédéric

PS : the dataset is created like this on the server:

CREATE UNLOGGED TABLE foo(a int);
INSERT INTO foo SELECT * FROM generate_series(1, 200000);
ALTER SYSTEM SET log_temp_files = 0;
ALTER SYSTEM SET log_min_duration_statement = -1
SELECT pg_reload_conf();

Attachment Content-Type Size
babar.py text/x-python 232 bytes
Babar.java text/x-java 1.0 KB

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