Remove read/sync fields from pg_stat_wal and GUC track_wal_io_timing

The four following attributes are removed from pg_stat_wal:
* wal_write
* wal_sync
* wal_write_time
* wal_sync_time

a051e71e28a1 has added an equivalent of this information in pg_stat_io
with more granularity as this now spreads across the backend types, IO
context and IO objects.  So, keeping the same information in pg_stat_wal
has little benefits.

Another benefit of this commit is the removal of PendingWalStats,
simplifying an upcoming patch to add per-backend WAL statistics, which
already support IO statistics and which have access to the write/sync
stats data of WAL.

The GUC track_wal_io_timing, that was used to enable or disable the
aggregation of the write and sync timings for WAL, is also removed.
pgstat_prepare_io_time() is simplified.

Bump catalog version.
Bump PGSTAT_FILE_FORMAT_ID, due to the update of PgStat_WalStats.

Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Discussion: https://postgr.es/m/Z7RkQ0EfYaqqjgz/@ip-10-97-1-34.eu-west-3.compute.internal

2 files changed, 0 insertions, 84 deletions

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 007746a4429..a8354576108 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -8393,28 +8393,6 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
       </listitem>
      </varlistentry>
 
-     <varlistentry id="guc-track-wal-io-timing" xreflabel="track_wal_io_timing">
-      <term><varname>track_wal_io_timing</varname> (<type>boolean</type>)
-      <indexterm>
-       <primary><varname>track_wal_io_timing</varname> configuration parameter</primary>
-      </indexterm>
-      </term>
-      <listitem>
-       <para>
-        Enables timing of WAL I/O calls. This parameter is off by default,
-        as it will repeatedly query the operating system for the current time,
-        which may cause significant overhead on some platforms.
-        You can use the <application>pg_test_timing</application> tool to
-        measure the overhead of timing on your system.
-        I/O timing information is
-        displayed in <link linkend="monitoring-pg-stat-wal-view">
-        <structname>pg_stat_wal</structname></link>.
-        Only superusers and users with the appropriate <literal>SET</literal>
-        privilege can change this setting.
-       </para>
-      </listitem>
-     </varlistentry>
-
      <varlistentry id="guc-track-functions" xreflabel="track_functions">
       <term><varname>track_functions</varname> (<type>enum</type>)
       <indexterm>
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index e698e74e116..3dfd059b7ee 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -184,11 +184,6 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
   </para>
 
   <para>
-   The parameter <xref linkend="guc-track-wal-io-timing"/> enables monitoring
-   of WAL write and fsync times.
-  </para>
-
-  <para>
    Normally these parameters are set in <filename>postgresql.conf</filename> so
    that they apply to all server processes, but it is possible to turn
    them on or off in individual sessions using the <xref
@@ -3267,63 +3262,6 @@ description | Waiting for a newly initialized WAL file to reach durable storage
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>wal_write</structfield> <type>bigint</type>
-      </para>
-      <para>
-       Number of times WAL buffers were written out to disk via
-       <function>XLogWrite</function> request.
-       See <xref linkend="wal-configuration"/> for more information about
-       the internal WAL function <function>XLogWrite</function>.
-      </para></entry>
-     </row>
-
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>wal_sync</structfield> <type>bigint</type>
-      </para>
-      <para>
-       Number of times WAL files were synced to disk via
-       <function>issue_xlog_fsync</function> request
-       (if <xref linkend="guc-fsync"/> is <literal>on</literal> and
-       <xref linkend="guc-wal-sync-method"/> is either
-       <literal>fdatasync</literal>, <literal>fsync</literal> or
-       <literal>fsync_writethrough</literal>, otherwise zero).
-       See <xref linkend="wal-configuration"/> for more information about
-       the internal WAL function <function>issue_xlog_fsync</function>.
-      </para></entry>
-     </row>
-
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>wal_write_time</structfield> <type>double precision</type>
-      </para>
-      <para>
-       Total amount of time spent writing WAL buffers to disk via
-       <function>XLogWrite</function> request, in milliseconds
-       (if <xref linkend="guc-track-wal-io-timing"/> is enabled,
-       otherwise zero).  This includes the sync time when
-       <varname>wal_sync_method</varname> is either
-       <literal>open_datasync</literal> or <literal>open_sync</literal>.
-      </para></entry>
-     </row>
-
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>wal_sync_time</structfield> <type>double precision</type>
-      </para>
-      <para>
-       Total amount of time spent syncing WAL files to disk via
-       <function>issue_xlog_fsync</function> request, in milliseconds
-       (if <varname>track_wal_io_timing</varname> is enabled,
-       <varname>fsync</varname> is <literal>on</literal>, and
-       <varname>wal_sync_method</varname> is either
-       <literal>fdatasync</literal>, <literal>fsync</literal> or
-       <literal>fsync_writethrough</literal>, otherwise zero).
-      </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>