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docs: Update HOT update docs for 19d8e2308b

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Commit 19d8e2308b changed when the HOT update optimization is possible
but neglected to update the Heap-Only Tuples (HOT) documentation.  This
patch updates that documentation accordingly.

Author: Elizabeth Christensen
Backpatch-through: 16
Reviewed-By: Stephen Frost, Alvaro Herrera
Discussion: https://postgr.es/m/CABoUFXRjisr58Ct_3VsFEdQx+fJeQTWTdJnM7XAp=8MUbtoa9A@mail.gmail.com
This commit is contained in:
Jeff Davis 2024-03-05 09:25:46 -08:00
parent c7ea3f4229
commit 7a9328e8e4
1 changed files with 11 additions and 10 deletions
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21
doc/src/sgml/storage.sgml
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@ -1097,8 +1097,10 @@ data. Empty in ordinary tables.</entry>
<itemizedlist> <itemizedlist>
<listitem> <listitem>
<para> <para>
The update does not modify any columns referenced by the table's The update does not modify any columns referenced by the table's indexes,
indexes, including expression and partial indexes. not including summarizing indexes. The only summarizing index method in
the core <productname>PostgreSQL</productname> distribution is <link
linkend="brin">BRIN</link>.
</para> </para>
</listitem> </listitem>
<listitem> <listitem>
@ -1114,7 +1116,8 @@ data. Empty in ordinary tables.</entry>
<itemizedlist> <itemizedlist>
<listitem> <listitem>
<para> <para>
New index entries are not needed to represent updated rows. New index entries are not needed to represent updated rows, however,
summary indexes may still need to be updated.
</para> </para>
</listitem> </listitem>
<listitem> <listitem>
@ -1130,14 +1133,12 @@ data. Empty in ordinary tables.</entry>
</para> </para>
<para> <para>
In summary, heap-only tuple updates can only be created You can increase the likelihood of sufficient page space for
if columns used by indexes are not updated. You can
increase the likelihood of sufficient page space for
<acronym>HOT</acronym> updates by decreasing a table's <link <acronym>HOT</acronym> updates by decreasing a table's <link
linkend="reloption-fillfactor"><literal>fillfactor</literal></link>. linkend="reloption-fillfactor"><literal>fillfactor</literal></link>. If you
If you don't, <acronym>HOT</acronym> updates will still happen because don't, <acronym>HOT</acronym> updates will still happen because new rows
new rows will naturally migrate to new pages and existing pages with will naturally migrate to new pages and existing pages with sufficient free
sufficient free space for new row versions. The system view <link space for new row versions. The system view <link
linkend="monitoring-pg-stat-all-tables-view">pg_stat_all_tables</link> linkend="monitoring-pg-stat-all-tables-view">pg_stat_all_tables</link>
allows monitoring of the occurrence of HOT and non-HOT updates. allows monitoring of the occurrence of HOT and non-HOT updates.
</para> </para>