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Count updates that move row to a new page.

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Add pgstat counter to track row updates that result in the successor
version going to a new heap page, leaving behind an original version
whose t_ctid points to the new version.  The current count is shown by
the n_tup_newpage_upd column of each of the pg_stat_*_tables views.

The new n_tup_newpage_upd column complements the existing n_tup_hot_upd
and n_tup_upd columns.  Tables that have high n_tup_newpage_upd values
(relative to n_tup_upd) are good candidates for tuning heap fillfactor.

Corey Huinker, with small tweaks by me.

Author: Corey Huinker <corey.huinker@gmail.com>
Reviewed-By: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CADkLM=ded21M9iZ36hHm-vj2rE2d=zcKpUQMds__Xm2pxLfHKA@mail.gmail.com
This commit is contained in:
Peter Geoghegan
2023-03-23 11:16:17 -07:00
parent 3b50275b12
commit ae4fdde135
9 changed files with 80 additions and 16 deletions
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28
doc/src/sgml/monitoring.sgml
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@ -4789,7 +4789,7 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
<structfield>n_tup_ins</structfield> <type>bigint</type>
</para>
<para>
Number of rows inserted
Total number of rows inserted
</para></entry>
</row>
@ -4798,7 +4798,10 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
<structfield>n_tup_upd</structfield> <type>bigint</type>
</para>
<para>
Number of rows updated (includes <link linkend="storage-hot">HOT updated rows</link>)
Total number of rows updated. (This includes row updates
counted in <structfield>n_tup_hot_upd</structfield> and
<structfield>n_tup_newpage_upd</structfield>, and remaining
non-<acronym>HOT</acronym> updates.)
</para></entry>
</row>
@ -4807,7 +4810,7 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
<structfield>n_tup_del</structfield> <type>bigint</type>
</para>
<para>
Number of rows deleted
Total number of rows deleted
</para></entry>
</row>
@ -4816,8 +4819,23 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
<structfield>n_tup_hot_upd</structfield> <type>bigint</type>
</para>
<para>
Number of rows HOT updated (i.e., with no separate index
update required)
Number of rows <link linkend="storage-hot">HOT updated</link>.
These are updates where no successor versions are required in
indexes.
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>n_tup_newpage_upd</structfield> <type>bigint</type>
</para>
<para>
Number of rows updated where the successor version goes onto a
<emphasis>new</emphasis> heap page, leaving behind an original
version with a
<link linkend="storage-tuple-layout"><structfield>t_ctid</structfield>
field</link> that points to a different heap page. These are
always non-<acronym>HOT</acronym> updates.
</para></entry>
</row>