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Commit9177545

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Make pg_createsubscriber warn if publisher has two-phase commit enabled.
pg_createsubscriber currently always sets up logical replicationwith two-phase commit disabled. Improving that is not going tohappen for v17. In the meantime, document the deficiency, andadjust pg_createsubscriber so that it will emit a warning ifthe source installation has max_prepared_transactions > 0.Hayato Kuroda (some mods by Amit Kapila and me), per complaint fromNoah MischDiscussion:https://postgr.es/m/20240623062157.97.nmisch@google.com
1 parentb3f5cce commit9177545

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2 files changed

+28
-17
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2 files changed

+28
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‎doc/src/sgml/ref/pg_createsubscriber.sgml

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Original file line numberDiff line numberDiff line change
@@ -353,6 +353,17 @@ PostgreSQL documentation
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<application>pg_createsubscriber</application>.
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</para>
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<para>
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<application>pg_createsubscriber</application> sets up logical
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replication with two-phase commit disabled. This means that any
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prepared transactions will be replicated at the time
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of <command>COMMIT PREPARED</command>, without advance preparation.
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Once setup is complete, you can manually drop and re-create the
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subscription(s) with
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the <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>
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option enabled.
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</para>
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<para>
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<application>pg_createsubscriber</application> changes the system
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identifier using <application>pg_resetwal</application>. It would avoid

‎src/bin/pg_basebackup/pg_createsubscriber.c

Lines changed: 17 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -823,6 +823,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
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intcur_repslots;
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intmax_walsenders;
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intcur_walsenders;
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intmax_prepared_transactions;
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pg_log_info("checking settings on publisher");
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@@ -849,23 +850,12 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
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* -----------------------------------------------------------------------
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*/
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res=PQexec(conn,
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"WITH wl AS "
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"(SELECT setting AS wallevel FROM pg_catalog.pg_settings "
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"WHERE name = 'wal_level'), "
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"total_mrs AS "
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"(SELECT setting AS tmrs FROM pg_catalog.pg_settings "
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"WHERE name = 'max_replication_slots'), "
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"cur_mrs AS "
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"(SELECT count(*) AS cmrs "
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"FROM pg_catalog.pg_replication_slots), "
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"total_mws AS "
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"(SELECT setting AS tmws FROM pg_catalog.pg_settings "
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"WHERE name = 'max_wal_senders'), "
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"cur_mws AS "
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"(SELECT count(*) AS cmws FROM pg_catalog.pg_stat_activity "
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"WHERE backend_type = 'walsender') "
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"SELECT wallevel, tmrs, cmrs, tmws, cmws "
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"FROM wl, total_mrs, cur_mrs, total_mws, cur_mws");
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"SELECT pg_catalog.current_setting('wal_level'),"
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" pg_catalog.current_setting('max_replication_slots'),"
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" (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
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" pg_catalog.current_setting('max_wal_senders'),"
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" (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
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" pg_catalog.current_setting('max_prepared_transactions')");
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if (PQresultStatus(res)!=PGRES_TUPLES_OK)
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{
@@ -879,6 +869,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
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cur_repslots=atoi(PQgetvalue(res,0,2));
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max_walsenders=atoi(PQgetvalue(res,0,3));
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cur_walsenders=atoi(PQgetvalue(res,0,4));
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max_prepared_transactions=atoi(PQgetvalue(res,0,5));
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PQclear(res);
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@@ -887,6 +878,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
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pg_log_debug("publisher: current replication slots: %d",cur_repslots);
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pg_log_debug("publisher: max_wal_senders: %d",max_walsenders);
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pg_log_debug("publisher: current wal senders: %d",cur_walsenders);
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pg_log_debug("publisher: max_prepared_transactions: %d",
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max_prepared_transactions);
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disconnect_database(conn, false);
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@@ -914,6 +907,13 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
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failed= true;
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}
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if (max_prepared_transactions!=0)
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{
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pg_log_warning("two_phase option will not be enabled for slots");
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pg_log_warning_detail("Subscriptions will be created with the two_phase option disabled. "
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"Prepared transactions will be replicated at COMMIT PREPARED.");
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}
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pg_free(wal_level);
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if (failed)

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