Track IO times in pg_stat_io

a9c70b46dbe and 8aaa04b32S added counting of IO operations to a new view,
pg_stat_io. Now, add IO timing for reads, writes, extends, and fsyncs to
pg_stat_io as well.

This combines the tracking for pgBufferUsage with the tracking for pg_stat_io
into a new function pgstat_count_io_op_time(). This should make it a bit
easier to avoid the somewhat costly instr_time conversion done for
pgBufferUsage.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Discussion: https://postgr.es/m/flat/CAAKRu_ay5iKmnbXZ3DsauViF3eMxu4m1oNnJXqV_HyqYeg55Ww%40mail.gmail.com

1 files changed, 59 insertions, 0 deletions

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index bce9ae46615..7da135d2f2f 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3817,6 +3817,18 @@ 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>read_time</structfield> <type>double precision</type>
+       </para>
+       <para>
+        Time spent in read operations in milliseconds (if
+        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
+       </para>
+      </entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry">
+       <para role="column_definition">
         <structfield>writes</structfield> <type>bigint</type>
        </para>
        <para>
@@ -3829,6 +3841,18 @@ 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>write_time</structfield> <type>double precision</type>
+       </para>
+       <para>
+        Time spent in write operations in milliseconds (if
+        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
+       </para>
+      </entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry">
+       <para role="column_definition">
         <structfield>extends</structfield> <type>bigint</type>
        </para>
        <para>
@@ -3841,6 +3865,18 @@ 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>extend_time</structfield> <type>double precision</type>
+       </para>
+       <para>
+        Time spent in extend operations in milliseconds (if
+        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
+       </para>
+      </entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry">
+       <para role="column_definition">
         <structfield>op_bytes</structfield> <type>bigint</type>
        </para>
        <para>
@@ -3916,6 +3952,18 @@ 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>fsync_time</structfield> <type>double precision</type>
+       </para>
+       <para>
+        Time spent in fsync operations in milliseconds (if
+        <xref linkend="guc-track-io-timing"/> is enabled, 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>
@@ -3978,6 +4026,17 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
    </itemizedlist>
   </para>
 
+  <note>
+   <para>
+    Columns tracking I/O time will only be non-zero when
+    <xref linkend="guc-track-io-timing"/> is enabled. The user should be
+    careful when referencing these columns in combination with their
+    corresponding IO operations in case <varname>track_io_timing</varname>
+    was not enabled for the entire time since the last stats reset.
+   </para>
+  </note>
+
+
 
  </sect2>