<!-- 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>