Fix assertion failure in snapshot building

danielgustafsson · danielgustafsson · commit 0f404c581247 · 2025-04-30T20:36:24.000+02:00
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 & This was originally committed as 48efb23 and backpatched down to v16, but since then there have been reports of this happening on v14 and v15 as well so this is a backpatch of 48efb23 down to 14. Bug: #17695 Author: Masahiko Sawada <sawada.mshk@gmail.com> Reviewed-by: Alexander Lakhin <exclusion@gmail.com> Reported-by: bowenshi <zxwsbg@qq.com> Reported-by: Alexander Pyhalov <a.pyhalov@postgrespro.ru> Reported-by: Teja Mupparti Discussion: https://postgr.es/m/17695-6be9277c9295985f@postgresql.org Backpatch-through: v14
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
@@ -2028,8 +2028,12 @@ 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;
