Add pg_stat_database counters for sessions and session time

This add counters for number of sessions, the different kind of session
termination types, and timers for how much time is spent in active vs
idle in a database to pg_stat_database.

Internally this also renames the parameter "force" to disconnect. This
was the only use-case for the parameter before, so repurposing it to
this mroe narrow usecase makes things cleaner than inventing something
new.

Author: Laurenz Albe
Reviewed-By: Magnus Hagander, Soumyadeep Chakraborty, Masahiro Ikeda
Discussion: https://postgr.es/m/b07e1f9953701b90c66ed368656f2aef40cac4fb.camel@cybertec.at

1 files changed, 77 insertions, 0 deletions

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 3cdb1aff3c8..f05140dd424 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3739,6 +3739,83 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>session_time</structfield> <type>double precision</type>
+      </para>
+      <para>
+       Time spent by database sessions in this database, in milliseconds
+       (note that statistics are only updated when the state of a session
+       changes, so if sessions have been idle for a long time, this idle time
+       won't be included)
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>active_time</structfield> <type>double precision</type>
+      </para>
+      <para>
+       Time spent executing SQL statements in this database, in milliseconds
+       (this corresponds to the states <literal>active</literal> and
+       <literal>fastpath function call</literal> in
+       <link linkend="monitoring-pg-stat-activity-view">
+       <structname>pg_stat_activity</structname></link>)
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>idle_in_transaction_time</structfield> <type>double precision</type>
+      </para>
+      <para>
+       Time spent idling while in a transaction in this database, in milliseconds
+       (this corresponds to the states <literal>idle in transaction</literal> and
+       <literal>idle in transaction (aborted)</literal> in
+       <link linkend="monitoring-pg-stat-activity-view">
+       <structname>pg_stat_activity</structname></link>)
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>sessions</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Total number of sessions established to this database
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>sessions_abandoned</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of database sessions to this database that were terminated
+       because connection to the client was lost
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>sessions_fatal</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of database sessions to this database that were terminated
+       by fatal errors
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>sessions_killed</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of database sessions to this database that were terminated
+       by operator intervention
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
       </para>
       <para>