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help / color / mirror / Atom feedFrom: Antonin Houska <ah@cybertec.at>
To: Alexander Lakhin <exclusion@gmail.com>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Amit Kapila <amit.kapila16@gmail.com>
Cc: Hayato Kuroda (Fujitsu) <kuroda.hayato@fujitsu.com>
Cc: Srinath Reddy Sadipiralla <srinath2133@gmail.com>
Cc: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>
Cc: Pg Hackers <pgsql-hackers@lists.postgresql.org>
Cc: Robert Treat <rob@xzilla.net>
Subject: Re: Adding REPACK [concurrently]
Date: Fri, 10 Apr 2026 12:57:47 +0200
Message-ID: <121156.1775818667@localhost> (raw)
In-Reply-To: <a38fc771-c860-4605-8c44-d16e8aff2534@gmail.com>
References: <202604072027.gazfa2zt2l2j@alvherre.pgsql>
<a38fc771-c860-4605-8c44-d16e8aff2534@gmail.com>
Alexander Lakhin <exclusion@gmail.com> wrote:
> Could you please look at an assertion failure produced by the following
> script, starting from 0d3dba38c:?
> createdb db1
> createdb db2
>
> echo "
> CREATE TABLE t0 (a text);
> BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
> INSERT INTO t0 VALUES ('a');
> SELECT pg_sleep(1);
> " | psql db1 &
>
> echo "
> CREATE TABLE t1 (id int PRIMARY KEY);
> CREATE TABLE t2 (id int PRIMARY KEY, a TEXT, FOREIGN KEY (id) REFERENCES t1);
> SET min_parallel_table_scan_size = 1;
> REPACK (CONCURRENTLY) t2;
> " | psql db2
> wait
>
> It triggers for me:
> TRAP: failed Assert("TransactionIdPrecedesOrEquals(TransactionXmin, RecentXmin)"), File: "procarray.c", Line: 2071, PID: 3529520
Attached is a fix that works for me.
Nevertheless, REPACK (CONCURRENTLY) in your test goes ahead only due to commit
0d3dba38c7, which will probably be reverted [1]. Then REPACK will wait for the
transaction in the other database (db1) to complete before it can actually
start.
Thanks for the report!
[1] https://www.postgresql.org/message-id/cdgw4sbbfcgk6du3iv54r2dgiy4tfywoklbotlmj4irxavdcr3@glxfw5jj277...
--
Antonin Houska
Web: https://www.cybertec-postgresql.com
Attachments:
[text/x-diff] 0001-Do-not-push-the-active-snapshot-for-copy_table_data-.patch (1.4K, ../121156.1775818667@localhost/2-0001-Do-not-push-the-active-snapshot-for-copy_table_data-.patch)
download | inline diff:
From 3fd0a70566f42d695b92c1cb2d26d3dbd5918a58 Mon Sep 17 00:00:00 2001
From: Antonin Houska <ah@cybertec.at>
Date: Fri, 10 Apr 2026 12:17:36 +0200
Subject: [PATCH] Do not push the active snapshot for copy_table_data before
it's needed.
make_new_heap() can launch parallel workers when building index on TOAST
relation. If the snapshot for copy_table_data() is already the active
snapshot, the workers can incorrectly consider it their transaction snapshot.
---
src/backend/commands/repack.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 58e3867246f..08fd132a4e3 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -1013,8 +1013,6 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
* Wait until the worker has the initial snapshot and retrieve it.
*/
snapshot = get_initial_snapshot(decoding_worker);
-
- PushActiveSnapshot(snapshot);
}
/* for CLUSTER or REPACK USING INDEX, mark the index as the one to use */
@@ -1038,6 +1036,8 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
NewHeap = table_open(OIDNewHeap, NoLock);
/* Copy the heap data into the new table in the desired order */
+ if (snapshot)
+ PushActiveSnapshot(snapshot);
copy_table_data(NewHeap, OldHeap, index, snapshot, verbose,
&swap_toast_by_content, &frozenXid, &cutoffMulti);
--
2.47.3
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Cc: ah@cybertec.at, exclusion@gmail.com, alvherre@alvh.no-ip.org, amit.kapila16@gmail.com, kuroda.hayato@fujitsu.com, srinath2133@gmail.com, mihailnikalayeu@gmail.com, boekewurm+postgres@gmail.com, pgsql-hackers@lists.postgresql.org, rob@xzilla.net
Subject: Re: Adding REPACK [concurrently]
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