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commit    48efb2302bea3b2af8b4bb865edcc70132ee4250
Author:   Daniel Gustafsson <dgustafsson@postgresql.org>
Date:     Tue Jul 04 15:36:13 2023 +0000

    Fix assertion failure in snapshot building
    
    Clear any potential stale next_phase_at value from the snapshot
    builder which otherwise may trip an assertion check ensuring
    that there is no next_phase_at value.
    
    This can be reproduced by running 80 concurrent sessions like
    the below where $c is a loop counter (assumes there has been
    1..$c databases created) :
    
      echo "
        CREATE TABLE replication_example(id SERIAL PRIMARY KEY,
                                         somedata int,
                                         text varchar(120));
        SELECT 'init' FROM
          pg_create_logical_replication_slot('regression_slot_$c',
                                             'test_decoding');
        SELECT data FROM
          pg_logical_slot_get_changes('regression_slot_$c', NULL,
                                      NULL, 'include-xids', '0',
                                      'skip-empty-xacts', '1');
      " | psql -d regress_$c >>psql.log &
    
    Backpatch down to v16.
    
    Bug: #17695
    Author: Masahiko Sawada <sawada.mshk@gmail.com>
    Reviewed-by: Alexander Lakhin <exclusion@gmail.com>
    Reported-by: bowenshi <zxwsbg@qq.com>
    Discussion: https://postgr.es/m/17695-6be9277c9295985f@postgresql.org
    Backpatch-through: v16


 src/backend/replication/logical/snapbuild.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index e403feeccda..843ceba840b 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1955,8 +1955,12 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	if (TransactionIdPrecedes(ondisk.builder.xmin, builder->initial_xmin_horizon))
 		goto snapshot_not_interesting;
 
-	/* consistent snapshots have no next phase */
+	/*
+	 * Consistent snapshots have no next phase. Reset next_phase_at as it is
+	 * possible that an old value may remain.
+	 */
 	Assert(ondisk.builder.next_phase_at == InvalidTransactionId);
+	builder->next_phase_at = InvalidTransactionId;
 
 	/* ok, we think the snapshot is sensible, copy over everything important */
 	builder->xmin = ondisk.builder.xmin;


[parent: 4b4798e1384c]