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-rw-r--r--doc/src/sgml/pgbench.sgml24
1 files changed, 24 insertions, 0 deletions
diff --git a/doc/src/sgml/pgbench.sgml b/doc/src/sgml/pgbench.sgml
index 437fceab2e4..91530abe5b0 100644
--- a/doc/src/sgml/pgbench.sgml
+++ b/doc/src/sgml/pgbench.sgml
@@ -317,6 +317,24 @@ pgbench <optional> <replaceable>options</> </optional> <replaceable>dbname</>
</varlistentry>
<varlistentry>
+ <term><option>--sampling-rate</option> <replaceable>rate</></term>
+ <listitem>
+ <para>
+ Sampling rate, used when writing data into the log, to reduce the
+ amount of log generated. If this option is given, only the specified
+ fraction of transactions are logged. 1.0 means all transactions will
+ be logged, 0.05 means only 5% of the transactions will be logged.
+ </para>
+ <para>
+ Remember to take the sampling rate into account when processing the
+ log file. For example, when computing tps values, you need to multiply
+ the numbers accordingly (e.g. with 0.01 sample rate, you'll only get
+ 1/100 of the actual tps).
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
<term><option>-M</option> <replaceable>querymode</></term>
<listitem>
<para>
@@ -750,6 +768,12 @@ END;
0 201 2513 0 1175850569 608
0 202 2038 0 1175850569 2663
</screen></para>
+
+ <para>
+ When running a long test on hardware that can handle a lot of transactions,
+ the log files can become very large. The <option>--sampling-rate</> option
+ can be used to log only a random sample of transactions.
+ </para>
</refsect2>
<refsect2>