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Make pg_createsubscriber warn if publisher has two-phase commit enabled.

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pg_createsubscriber currently always sets up logical replication
with two-phase commit disabled.  Improving that is not going to
happen for v17.  In the meantime, document the deficiency, and
adjust pg_createsubscriber so that it will emit a warning if
the source installation has max_prepared_transactions > 0.

Hayato Kuroda (some mods by Amit Kapila and me), per complaint from
Noah Misch

Discussion: https://postgr.es/m/20240623062157.97.nmisch@google.com
This commit is contained in:
Tom Lane 2024-06-30 14:24:14 -04:00
parent b3f5ccebd7
commit 917754557c
2 changed files with 28 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
doc/src/sgml/ref/pg_createsubscriber.sgml
View File

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

34
src/bin/pg_basebackup/pg_createsubscriber.c
View File

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