Fix duplicate transaction replay during pg_createsubscriber.

Amit Kapila · Amit Kapila · commit e1c3654839e4 · 2025-07-24T09:05:32.000Z
Previously, the tool could replay the same transaction twice, once during recovery, then again during replication after the subscriber was set up. This occurred because the same recovery_target_lsn was used both to finalize recovery and to start replication. If recovery_target_inclusive = true, the transaction at that LSN would be applied during recovery and then sent again by the publisher leading to duplication. To prevent this, we now set recovery_target_inclusive = false. This ensures the transaction at recovery_target_lsn is not reapplied during recovery, avoiding duplication when replication begins. Bug #18897 Reported-by: Zane Duffield <duffieldzane@gmail.com> Author: Shlok Kyal <shlok.kyal.oss@gmail.com> Reviewed-by: vignesh C <vignesh21@gmail.com> Reviewed-by: Amit Kapila <amit.kapila16@gmail.com> Backpatch-through: 17, where it was introduced Discussion: https://postgr.es/m/18897-d3db67535860dddb@postgresql.org
diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -1250,8 +1250,17 @@ setup_recovery(const struct LogicalRepInfo *dbinfo, const char *datadir, const c
 	appendPQExpBufferStr(recoveryconfcontents, "recovery_target = ''\n");
 	appendPQExpBufferStr(recoveryconfcontents,
 						 "recovery_target_timeline = 'latest'\n");
+
+	/*
+	 * Set recovery_target_inclusive = false to avoid reapplying the
+	 * transaction committed at 'lsn' after subscription is enabled. This is
+	 * because the provided 'lsn' is also used as the replication start point
+	 * for the subscription. So, the server can send the transaction committed
+	 * at that 'lsn' after replication is started which can lead to applying
+	 * the same transaction twice if we keep recovery_target_inclusive = true.
+	 */
 	appendPQExpBufferStr(recoveryconfcontents,
-						 "recovery_target_inclusive = true\n");
+						 "recovery_target_inclusive = false\n");
 	appendPQExpBufferStr(recoveryconfcontents,
 						 "recovery_target_action = promote\n");
 	appendPQExpBufferStr(recoveryconfcontents, "recovery_target_name = ''\n");
