Horton

effective_wal_level is not decreasing after using REPACK (CONCURRENTLY)

Imran Zaheer <imran.zhir@gmail.com>

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From: Imran Zaheer <imran.zhir@gmail.com>
To: pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2026-05-21T16:32:36Z
Lists: pgsql-hackers

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  1. Fix 051_effective_wal_level.pl on builds without injection points.

  2. Disable logical decoding after REPACK (CONCURRENTLY)

Attachments

Hi

The recent support for dynamic toggling of logical decoding (67c2097)
disables logical
decoding if no logical slots are present. But the repack command doesn't seem to
coordinate with this toggling. The effective_wal_level is not
decreasing after using repack concurrently.

postgres=# show effective_wal_level;
 effective_wal_level
---------------------
 replica
(1 row)

postgres=# create table foo(a int primary key);
CREATE TABLE
postgres=# REPACK (CONCURRENTLY) foo;
2026-05-21 20:46:25.423 PKT [1591896] LOG:  logical decoding is
enabled upon creating a new logical replication slot
2026-05-21 20:46:25.634 PKT [1591896] LOG:  logical decoding found
consistent point at 0/018F36D0
2026-05-21 20:46:25.634 PKT [1591896] DETAIL:  There are no running
transactions.
REPACK
postgres=# select slot_name from pg_replication_slots;
 slot_name
-----------
(0 rows)

postgres=# show effective_wal_level;
 effective_wal_level
---------------------
 logical
(1 row)


The server has to be restarted in order to decrease the
effective_wal_level. REPACK CONCURRENTLY uses a temporary slot that is
dropped at the time of cleanup,  but logical decoding is not disabled.

This may be related to both commits, 28d534e and 67c2097

The attached patch adds the `RequestDisableLogicalDecoding` call to
`repack_cleanup_logical_decoding` after the replication slot is
dropped so the checkpointer will take care of it..


Thanks
Imran Zaheer