From: Jochen Bandhauer <jb@jbitc.de>
To: pgsql-bugs@lists.postgresql.org
Subject: on 19beta3: repack (concurrently) affects sessions with transaction isolation level repeatable read
Date: Sat, 22 Aug 2026 09:29:41 +0200
Message-ID: <5d2060d5-8145-40c6-9a2e-4ddb9f6b0fc9@jbitc.de> (raw)
Hello,
while using repack (concurrently) I found a behavior that I didn't
expect. When running a "repack (concurrently) t;" in one session,
another session with "transaction isolation level repeatable read"
reports sometimes 0 for "select count(*) from t;".
PostgreSQL Version: PostgreSQL 19beta3 on x86_64-pc-linux-gnu, compiled
by gcc (GCC) 14.3.1 20251022 (Red Hat 14.3.1-4), 64-bit
configure command: ./configure --prefix=/home/postgres/pginstall
OS: Red Hat Enterprise Linux 10.2 (Coughlan)
uname -a: Linux lin8.fritz.box 6.12.0-211.44.1.el10_2.x86_64 #1 SMP
PREEMPT_DYNAMIC Tue Aug 4 03:10:19 EDT 2026 x86_64 GNU/Linux
Test Case:
-- create table
drop table if exists t;
create table t (
col1 bigint primary key,
col2 text default 'default text'
);
insert into t (col1) select g from generate_series(1, 10000) as g;
Session 1 runs from time to time: repack (concurrently) t;
Session 2 runs the following script with: while true; do psql mydb -f
./s2.sql; sleep 0.1; done| grep -v "^$"
Script s2.sql:
\pset tuples_only on
\o /dev/null
begin;
set transaction isolation level repeatable read;
select 1;
select pg_sleep(1);
\o
select count(*) from t;
\o /dev/null
end;
Output Session 2:
10000
10000
0
10000
10000
0
10000
10000
10000
0
10000
10000
0
10000
0 always when Session 1 runs: repack (concurrently) t;
Expected Output: Always 10000
Only the (concurrently) option shows this behavior. Wehen using "repack
t;" or "repack t using index t_pkey;" the output is always 10000.
Thanks
Jochen
--
Mit freundlichen Grüßen
Jochen Bandhauer
+49 (0)176 29390012
www.jbitc.de
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Subject: Re: on 19beta3: repack (concurrently) affects sessions with transaction isolation level repeatable read
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