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doc: Update \timing and add LAST_QUERY_MS variable documentation #12

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doc: Update \timing and add LAST_QUERY_MS variable documentation #12

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38 changes: 38 additions & 0 deletions doc/src/sgml/ref/psql-ref.sgml
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Original file line number Diff line number Diff line change
Expand Up @@ -3836,6 +3836,14 @@ SELECT 1 \bind \sendpipeline
1 second are also shown in minutes:seconds format, with hours and
days fields added if needed.
</para>
<para>
Note that query execution time is always measured regardless of the
<literal>\timing</literal> setting. The <literal>\timing</literal> command
only controls whether the timing information is displayed. The measured
time is always available in the <varname>LAST_QUERY_MS</varname> variable
(see <xref linkend="app-psql-variables-last-query-ms"/>), which allows
scripts to access timing data programmatically without cluttering output.
</para>
</listitem>
</varlistentry>

Expand Down Expand Up @@ -4536,6 +4544,36 @@ bar
</listitem>
</varlistentry>

<varlistentry id="app-psql-variables-last-query-ms">
<term><varname>LAST_QUERY_MS</varname></term>
<listitem>
<para>
The execution time of the most recent SQL statement, measured in
milliseconds and stored as a decimal number with three decimal places.
This variable is always updated after each query execution, regardless of
the <literal>\timing</literal> setting. The <literal>\timing</literal>
command only controls whether the timing is displayed; measurement
always occurs.
</para>
<para>
The variable is initialized to <literal>0</literal> at the start of each
<application>psql</application> session. This allows scripts to access
query timing programmatically for conditional logic or logging without
displaying timing information in the output.
</para>
<para>
Example:
<programlisting>
\timing off
SELECT expensive_operation();
\if :LAST_QUERY_MS > 1000
\echo 'WARNING: Query took more than 1 second'
\endif
</programlisting>
</para>
</listitem>
</varlistentry>

<varlistentry id="app-psql-variables-on-error-rollback">
<term>
<varname>ON_ERROR_ROLLBACK</varname>
Expand Down