Prevent startup of logical replication launcher during pg_upgrade

The logical replication launcher may start apply workers during an
upgrade.  This could be the cause of corruptions on a new cluster if
these are able to apply changes before the physical files are copied
over to the new cluster.

The chance of being able to do so is small as pg_upgrade uses its own
port and unix domain directory (the latter is customizable with
--socketdir), but just preventing the launcher to start is safer at the
end, because we are then sure that no changes will be applied.  Like
29d0a77fa660 for max_slot_wal_keep_size, this is only set when a cluster
uses v17 or newer.

Author: Vignesh C
Discussion: https://postgr.es/m/CALDaNm2g9ZKf=y8X6z6MsLCuh8WwU-=Q6pLj35NFi2M5BZNS_A@mail.gmail.com

diff --git a/src/bin/pg_upgrade/server.c b/src/bin/pg_upgrade/server.c
index d7f6c268ef4c65ad46893e4a08154a423d86cda1..c24c5f69fcb77147d448c1f70eb4622eb0adfd0a 100644 (file)
--- a/src/bin/pg_upgrade/server.c
+++ b/src/bin/pg_upgrade/server.c
@@ -248,9 +248,17 @@ start_postmaster(ClusterInfo *cluster, bool report_and_exit_on_error)
         * invalidation of slots during the upgrade. We set this option when
         * cluster is PG17 or later because logical replication slots can only be
         * migrated since then. Besides, max_slot_wal_keep_size is added in PG13.
+        *
+        * Use max_logical_replication_workers as 0 to prevent a startup of the
+        * logical replication launcher while upgrading because it may start apply
+        * workers that could start receiving changes from the publisher before
+        * the physical files are put in place, causing corruption on the new
+        * cluster upgrading to.  Like the previous parameter, this is set only
+        * when a cluster is PG17 or later as logical slots can only be migrated
+        * since this version.
         */
        if (GET_MAJOR_VERSION(cluster->major_version) >= 1700)
-               appendPQExpBufferStr(&pgoptions, " -c max_slot_wal_keep_size=-1");
+               appendPQExpBufferStr(&pgoptions, " -c max_slot_wal_keep_size=-1 -c max_logical_replication_workers=0");
 
        /* Use -b to disable autovacuum. */
        snprintf(cmd, sizeof(cmd),