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commit    9fd8b331dfe151b7c833e2c8fa17ce753830b891
Author:   Amit Kapila <akapila@postgresql.org>
Date:     Fri Jul 12 03:59:21 2024 +0000
First released in: 18.0, 17.0

    Fix unstable test in 040_pg_createsubscriber.
    
    The slot synchronization failed because the local slot's (created during
    slot synchronization) catalog_xmin on standby is ahead of remote slot.
    This happens because the INSERT before slot synchronization results in the
    generation of a new xid that could be replicated to the standby. Now
    before the xmin of the physical slot on the primary catches up via
    hot_standby_feedback, the test has created a logical slot that got some
    prior value of catalog_xmin.
    
    To fix this we could try to ensure that the physical slot's catalog_xmin
    is caught up to latest value before creating a logical slot but we took a
    simpler path to move the INSERT after synchronizing the logical slot.
    
    Reported-by: Alexander Lakhin as per buildfarm
    Diagnosed-by: Amit Kapila, Hou Zhijie, Alexander Lakhin
    Author: Hou Zhijie
    Backpatch-through: 17
    Discussion: https://postgr.es/m/bde6ac67-69cc-c104-5ab6-dd4f5deadf24@gmail.com


 src/bin/pg_basebackup/t/040_pg_createsubscriber.pl | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index 74b90d9a913..bb121271570 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -227,10 +227,6 @@ command_fails(
 	],
 	'primary server is in recovery');
 
-# Insert another row on node P and wait node S to catch up
-$node_p->safe_psql($db1, "INSERT INTO tbl1 VALUES('second row')");
-$node_p->wait_for_replay_catchup($node_s);
-
 # Check some unmet conditions on node P
 $node_p->append_conf(
 	'postgresql.conf', q{
@@ -306,6 +302,14 @@ my $result = $node_s->safe_psql('postgres',
 );
 is($result, 'failover_slot', 'failover slot is synced');
 
+# Insert another row on node P and wait node S to catch up. We
+# intentionally performed this insert after syncing logical slot
+# as otherwise the local slot's (created during synchronization of
+# slot) xmin on standby could be ahead of the remote slot leading
+# to failure in synchronization.
+$node_p->safe_psql($db1, "INSERT INTO tbl1 VALUES('second row')");
+$node_p->wait_for_replay_catchup($node_s);
+
 # Create subscription to test its removal
 my $dummy_sub = 'regress_sub_dummy';
 $node_p->safe_psql($db1,


[parent: 22d946b0f86f]