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Commit03b08c8

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author
Amit Kapila
committed
pg_createsubscriber: Fix an unpredictable recovery wait time.
The problem is that the tool is using the LSN returned bypg_create_logical_replication_slot() as recovery_target_lsn. This LSN isahead of the current WAL position and the recovery waits until thepublisher writes a WAL record to reach the target and ends the recovery.On idle systems, this wait time is unpredictable and could lead to failurein promoting the subscriber. To avoid that, insert a harmless WAL record.Reported-by: Alexander Lakhin and Tom LaneDiagnosed-by: Hayato KurodaAuthor: Euler TaveiraReviewed-by: Hayato Kuroda, Amit KapilaBackpatch-through: 17Discussion:https://postgr.es/m/2377319.1719766794%40sss.pgh.pa.usDiscussion:https://postgr.es/m/CA+TgmoYcY+Wb67NAwaHT7MvxCSeV86oSc+va9hHKaasE42ukyw@mail.gmail.com
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‎src/bin/pg_basebackup/pg_createsubscriber.c

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Original file line numberDiff line numberDiff line change
@@ -778,6 +778,28 @@ setup_publisher(struct LogicalRepInfo *dbinfo)
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else
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exit(1);
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/*
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* Since we are using the LSN returned by the last replication slot as
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* recovery_target_lsn, this LSN is ahead of the current WAL position
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* and the recovery waits until the publisher writes a WAL record to
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* reach the target and ends the recovery. On idle systems, this wait
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* time is unpredictable and could lead to failure in promoting the
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* subscriber. To avoid that, insert a harmless WAL record.
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*/
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if (i==num_dbs-1&& !dry_run)
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{
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PGresult*res;
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res=PQexec(conn,"SELECT pg_log_standby_snapshot()");
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if (PQresultStatus(res)!=PGRES_TUPLES_OK)
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{
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pg_log_error("could not write an additional WAL record: %s",
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PQresultErrorMessage(res));
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disconnect_database(conn, true);
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}
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PQclear(res);
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}
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disconnect_database(conn, false);
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}
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