From 26669757b6a7665c1069e77e6472bd8550193ca6 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Fri, 7 Apr 2023 23:11:28 -0700
Subject: Handle logical slot conflicts on standby
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During WAL replay on the standby, when a conflict with a logical slot is
identified, invalidate such slots. There are two sources of conflicts:
1) Using the information added in 6af1793954e, logical slots are invalidated if
   required rows are removed
2) wal_level on the primary server is reduced to below logical

Uses the infrastructure introduced in the prior commit. FIXME: add commit
reference.

Change InvalidatePossiblyObsoleteSlot() to use a recovery conflict to
interrupt use of a slot, if called in the startup process. The new recovery
conflict is added to pg_stat_database_conflicts, as confl_active_logicalslot.

See 6af1793954e for an overall design of logical decoding on a standby.

Bumps catversion for the addition of the pg_stat_database_conflicts column.
Bumps PGSTAT_FILE_FORMAT_ID for the same reason.

Author: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
Author: Andres Freund <andres@anarazel.de>
Author: Amit Khandekar <amitdkhan.pg@gmail.com> (in an older version)
Reviewed-by: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Fabrízio de Royes Mello <fabriziomello@gmail.com>
Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/20230407075009.igg7be27ha2htkbt@awork3.anarazel.de
---
 doc/src/sgml/monitoring.sgml | 11 +++++++++++
 1 file changed, 11 insertions(+)

(limited to 'doc')

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 0eaff70dcb..e8ab803267 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -4742,6 +4742,17 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
        deadlocks
       </para></entry>
      </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>confl_active_logicalslot</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of uses of logical slots in this database that have been
+       canceled due to old snapshots or a too low <xref linkend="guc-wal-level"/>
+       on the primary
+      </para></entry>
+     </row>
     </tbody>
    </tgroup>
   </table>
-- 
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