Track invalidation_reason in pg_replication_slots.

Till now, the reason for replication slot invalidation is not tracked
directly in pg_replication_slots. A recent commit 007693f2a3 added
'conflict_reason' to show the reasons for slot conflict/invalidation, but
only for logical slots.

This commit adds a new column 'invalidation_reason' to show invalidation
reasons for both physical and logical slots. And, this commit also turns
'conflict_reason' text column to 'conflicting' boolean column (effectively
reverting commit 007693f2a3). The 'conflicting' column is true for
invalidation reasons 'rows_removed' and 'wal_level_insufficient' because
those make the slot conflict with recovery. When 'conflicting' is true,
one can now look at the new 'invalidation_reason' column for the reason
for the logical slot's conflict with recovery.

The new 'invalidation_reason' column will also be useful to track other
invalidation reasons in the future commit.

Author: Bharath Rupireddy
Reviewed-by: Bertrand Drouvot, Amit Kapila, Shveta Malik
Discussion: https://www.postgresql.org/message-id/ZfR7HuzFEswakt/a%40ip-10-97-1-34.eu-west-3.compute.internal
Discussion: https://www.postgresql.org/message-id/CALj2ACW4aUe-_uFQOjdWCEN-xXoLGhmvRFnL8SNw_TZ5nJe+aw@mail.gmail.com

2 files changed, 20 insertions, 9 deletions

diff --git a/doc/src/sgml/ref/pgupgrade.sgml b/doc/src/sgml/ref/pgupgrade.sgml
index 58c6c2df8b8..8de52bf7527 100644
--- a/doc/src/sgml/ref/pgupgrade.sgml
+++ b/doc/src/sgml/ref/pgupgrade.sgml
@@ -453,8 +453,8 @@ make prefix=/usr/local/pgsql.new install
       <para>
        All slots on the old cluster must be usable, i.e., there are no slots
        whose
-       <link linkend="view-pg-replication-slots">pg_replication_slots</link>.<structfield>conflict_reason</structfield>
-       is not <literal>NULL</literal>.
+       <link linkend="view-pg-replication-slots">pg_replication_slots</link>.<structfield>conflicting</structfield>
+       is not <literal>true</literal>.
       </para>
      </listitem>
      <listitem>
diff --git a/doc/src/sgml/system-views.sgml b/doc/src/sgml/system-views.sgml
index be90edd0e20..b5da476c206 100644
--- a/doc/src/sgml/system-views.sgml
+++ b/doc/src/sgml/system-views.sgml
@@ -2525,13 +2525,24 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>conflict_reason</structfield> <type>text</type>
+       <structfield>conflicting</structfield> <type>bool</type>
       </para>
       <para>
-       The reason for the logical slot's conflict with recovery. It is always
-       NULL for physical slots, as well as for logical slots which are not
-       invalidated. The non-NULL values indicate that the slot is marked
-       as invalidated. Possible values are:
+       True if this logical slot conflicted with recovery (and so is now
+       invalidated). When this column is true, check
+       <structfield>invalidation_reason</structfield> column for the conflict
+       reason. Always NULL for physical slots.
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>invalidation_reason</structfield> <type>text</type>
+      </para>
+      <para>
+       The reason for the slot's invalidation. It is set for both logical and
+       physical slots. <literal>NULL</literal> if the slot is not invalidated.
+       Possible values are:
        <itemizedlist spacing="compact">
         <listitem>
          <para>
@@ -2542,14 +2553,14 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
         <listitem>
          <para>
           <literal>rows_removed</literal> means that the required rows have
-          been removed.
+          been removed. It is set only for logical slots.
          </para>
         </listitem>
         <listitem>
          <para>
           <literal>wal_level_insufficient</literal> means that the
           primary doesn't have a <xref linkend="guc-wal-level"/> sufficient to
-          perform logical decoding.
+          perform logical decoding.  It is set only for logical slots.
          </para>
         </listitem>
        </itemizedlist>