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<!-- doc/src/sgml/tsm-system-time.sgml -->
<sect1 id="tsm-system-time" xreflabel="tsm_system_time">
<title>tsm_system_time</title>
<indexterm zone="tsm-system-time">
<primary>tsm_system_time</primary>
</indexterm>
<para>
The <filename>tsm_system_time</> module provides the tablesample method
<literal>SYSTEM_TIME</literal>, which can be used inside the
<command>TABLESAMPLE</command> clause of a <command>SELECT</command>.
</para>
<para>
This tablesample method uses a linear probing algorithm to read sample
of a table and uses time in milliseconds as limit (unlike the
<literal>SYSTEM</literal> tablesample method which limits by percentage
of a table). This gives you some control over the length of execution
of your query.
</para>
<sect2>
<title>Examples</title>
<para>
Here is an example of selecting sample of a table with
<literal>SYSTEM_TIME</>. First install the extension:
</para>
<programlisting>
CREATE EXTENSION tsm_system_time;
</programlisting>
<para>
Then you can use it in a <command>SELECT</command> command the same way as
other tablesample methods:
<programlisting>
SELECT * FROM my_table TABLESAMPLE SYSTEM_TIME(1000);
</programlisting>
</para>
<para>
The above command will return as large a sample of my_table as it can read in
1 second (or less if it reads whole table faster).
</para>
</sect2>
</sect1>
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