1890 lines
73 KiB
Plaintext
1890 lines
73 KiB
Plaintext
<!-- doc/src/sgml/ref/pgbench.sgml -->
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<refentry id="pgbench">
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<indexterm zone="pgbench">
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<primary>pgbench</primary>
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</indexterm>
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<refmeta>
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<refentrytitle><application>pgbench</application></refentrytitle>
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<manvolnum>1</manvolnum>
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<refmiscinfo>Application</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>pgbench</refname>
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<refpurpose>run a benchmark test on <productname>PostgreSQL</productname></refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command>pgbench</command>
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<arg choice="plain"><option>-i</option></arg>
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<arg rep="repeat"><replaceable>option</replaceable></arg>
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<arg choice="opt"><replaceable>dbname</replaceable></arg>
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</cmdsynopsis>
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<cmdsynopsis>
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<command>pgbench</command>
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<arg rep="repeat"><replaceable>option</replaceable></arg>
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<arg choice="opt"><replaceable>dbname</replaceable></arg>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>
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<application>pgbench</application> is a simple program for running benchmark
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tests on <productname>PostgreSQL</productname>. It runs the same sequence of SQL
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commands over and over, possibly in multiple concurrent database sessions,
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and then calculates the average transaction rate (transactions per second).
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By default, <application>pgbench</application> tests a scenario that is
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loosely based on TPC-B, involving five <command>SELECT</command>,
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<command>UPDATE</command>, and <command>INSERT</command> commands per transaction.
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However, it is easy to test other cases by writing your own transaction
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script files.
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</para>
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<para>
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Typical output from <application>pgbench</application> looks like:
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<screen>
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transaction type: <builtin: TPC-B (sort of)>
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scaling factor: 10
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query mode: simple
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number of clients: 10
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number of threads: 1
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number of transactions per client: 1000
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number of transactions actually processed: 10000/10000
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tps = 85.184871 (including connections establishing)
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tps = 85.296346 (excluding connections establishing)
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</screen>
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The first six lines report some of the most important parameter
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settings. The next line reports the number of transactions completed
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and intended (the latter being just the product of number of clients
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and number of transactions per client); these will be equal unless the run
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failed before completion. (In <option>-T</option> mode, only the actual
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number of transactions is printed.)
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The last two lines report the number of transactions per second,
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figured with and without counting the time to start database sessions.
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</para>
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<para>
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The default TPC-B-like transaction test requires specific tables to be
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set up beforehand. <application>pgbench</application> should be invoked with
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the <option>-i</option> (initialize) option to create and populate these
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tables. (When you are testing a custom script, you don't need this
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step, but will instead need to do whatever setup your test needs.)
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Initialization looks like:
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<programlisting>
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pgbench -i <optional> <replaceable>other-options</replaceable> </optional> <replaceable>dbname</replaceable>
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</programlisting>
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where <replaceable>dbname</replaceable> is the name of the already-created
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database to test in. (You may also need <option>-h</option>,
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<option>-p</option>, and/or <option>-U</option> options to specify how to
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connect to the database server.)
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</para>
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<caution>
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<para>
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<literal>pgbench -i</literal> creates four tables <structname>pgbench_accounts</structname>,
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<structname>pgbench_branches</structname>, <structname>pgbench_history</structname>, and
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<structname>pgbench_tellers</structname>,
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destroying any existing tables of these names.
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Be very careful to use another database if you have tables having these
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names!
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</para>
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</caution>
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<para>
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At the default <quote>scale factor</quote> of 1, the tables initially
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contain this many rows:
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<screen>
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table # of rows
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---------------------------------
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pgbench_branches 1
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pgbench_tellers 10
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pgbench_accounts 100000
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pgbench_history 0
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</screen>
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You can (and, for most purposes, probably should) increase the number
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of rows by using the <option>-s</option> (scale factor) option. The
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<option>-F</option> (fillfactor) option might also be used at this point.
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</para>
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<para>
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Once you have done the necessary setup, you can run your benchmark
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with a command that doesn't include <option>-i</option>, that is
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<programlisting>
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pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>dbname</replaceable>
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</programlisting>
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In nearly all cases, you'll need some options to make a useful test.
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The most important options are <option>-c</option> (number of clients),
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<option>-t</option> (number of transactions), <option>-T</option> (time limit),
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and <option>-f</option> (specify a custom script file).
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See below for a full list.
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</para>
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</refsect1>
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<refsect1>
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<title>Options</title>
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<para>
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The following is divided into three subsections. Different options are
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used during database initialization and while running benchmarks, but some
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options are useful in both cases.
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</para>
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<refsect2 id="pgbench-init-options">
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<title>Initialization Options</title>
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<para>
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<application>pgbench</application> accepts the following command-line
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initialization arguments:
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<variablelist>
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<varlistentry>
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<term><option>-i</option></term>
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<term><option>--initialize</option></term>
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<listitem>
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<para>
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Required to invoke initialization mode.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-I <replaceable>init_steps</replaceable></option></term>
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<term><option>--init-steps=<replaceable>init_steps</replaceable></option></term>
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<listitem>
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<para>
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Perform just a selected set of the normal initialization steps.
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<replaceable>init_steps</replaceable> specifies the
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initialization steps to be performed, using one character per step.
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Each step is invoked in the specified order.
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The default is <literal>dtgvp</literal>.
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The available steps are:
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<variablelist>
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<varlistentry>
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<term><literal>d</literal> (Drop)</term>
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<listitem>
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<para>
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Drop any existing <application>pgbench</application> tables.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>t</literal> (create Tables)</term>
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<listitem>
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<para>
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Create the tables used by the
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standard <application>pgbench</application> scenario, namely
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<structname>pgbench_accounts</structname>,
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<structname>pgbench_branches</structname>,
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<structname>pgbench_history</structname>, and
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<structname>pgbench_tellers</structname>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>g</literal> (Generate data)</term>
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<listitem>
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<para>
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Generate data and load it into the standard tables,
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replacing any data already present.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>v</literal> (Vacuum)</term>
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<listitem>
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<para>
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Invoke <command>VACUUM</command> on the standard tables.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>p</literal> (create Primary keys)</term>
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<listitem>
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<para>
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Create primary key indexes on the standard tables.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>f</literal> (create Foreign keys)</term>
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<listitem>
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<para>
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Create foreign key constraints between the standard tables.
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(Note that this step is not performed by default.)
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-F</option> <replaceable>fillfactor</replaceable></term>
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<term><option>--fillfactor=</option><replaceable>fillfactor</replaceable></term>
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<listitem>
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<para>
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Create the <structname>pgbench_accounts</structname>,
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<structname>pgbench_tellers</structname> and
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<structname>pgbench_branches</structname> tables with the given fillfactor.
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Default is 100.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-n</option></term>
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<term><option>--no-vacuum</option></term>
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<listitem>
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<para>
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Perform no vacuuming during initialization.
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(This option suppresses the <literal>v</literal> initialization step,
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even if it was specified in <option>-I</option>.)
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-q</option></term>
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<term><option>--quiet</option></term>
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<listitem>
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<para>
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Switch logging to quiet mode, producing only one progress message per 5
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seconds. The default logging prints one message each 100000 rows, which
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often outputs many lines per second (especially on good hardware).
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-s</option> <replaceable>scale_factor</replaceable></term>
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<term><option>--scale=</option><replaceable>scale_factor</replaceable></term>
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<listitem>
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<para>
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Multiply the number of rows generated by the scale factor.
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For example, <literal>-s 100</literal> will create 10,000,000 rows
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in the <structname>pgbench_accounts</structname> table. Default is 1.
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When the scale is 20,000 or larger, the columns used to
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hold account identifiers (<structfield>aid</structfield> columns)
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will switch to using larger integers (<type>bigint</type>),
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in order to be big enough to hold the range of account
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identifiers.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--foreign-keys</option></term>
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<listitem>
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<para>
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Create foreign key constraints between the standard tables.
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(This option adds the <literal>f</literal> step to the initialization
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step sequence, if it is not already present.)
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--index-tablespace=<replaceable>index_tablespace</replaceable></option></term>
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<listitem>
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<para>
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Create indexes in the specified tablespace, rather than the default
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tablespace.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--tablespace=<replaceable>tablespace</replaceable></option></term>
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<listitem>
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<para>
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Create tables in the specified tablespace, rather than the default
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tablespace.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--unlogged-tables</option></term>
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<listitem>
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<para>
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Create all tables as unlogged tables, rather than permanent tables.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect2>
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<refsect2 id="pgbench-run-options">
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<title>Benchmarking Options</title>
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<para>
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<application>pgbench</application> accepts the following command-line
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benchmarking arguments:
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<variablelist>
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<varlistentry>
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<term><option>-b</option> <replaceable>scriptname[@weight]</replaceable></term>
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<term><option>--builtin</option>=<replaceable>scriptname[@weight]</replaceable></term>
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<listitem>
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<para>
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Add the specified built-in script to the list of executed scripts.
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An optional integer weight after <literal>@</literal> allows to adjust the
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probability of drawing the script. If not specified, it is set to 1.
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Available built-in scripts are: <literal>tpcb-like</literal>,
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<literal>simple-update</literal> and <literal>select-only</literal>.
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Unambiguous prefixes of built-in names are accepted.
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With special name <literal>list</literal>, show the list of built-in scripts
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and exit immediately.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-c</option> <replaceable>clients</replaceable></term>
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<term><option>--client=</option><replaceable>clients</replaceable></term>
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<listitem>
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<para>
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Number of clients simulated, that is, number of concurrent database
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sessions. Default is 1.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-C</option></term>
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<term><option>--connect</option></term>
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<listitem>
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<para>
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Establish a new connection for each transaction, rather than
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doing it just once per client session.
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This is useful to measure the connection overhead.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-d</option></term>
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<term><option>--debug</option></term>
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<listitem>
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<para>
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Print debugging output.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-D</option> <replaceable>varname</replaceable><literal>=</literal><replaceable>value</replaceable></term>
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<term><option>--define=</option><replaceable>varname</replaceable><literal>=</literal><replaceable>value</replaceable></term>
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<listitem>
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<para>
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Define a variable for use by a custom script (see below).
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Multiple <option>-D</option> options are allowed.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-f</option> <replaceable>filename[@weight]</replaceable></term>
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<term><option>--file=</option><replaceable>filename[@weight]</replaceable></term>
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<listitem>
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<para>
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Add a transaction script read from <replaceable>filename</replaceable> to
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the list of executed scripts.
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An optional integer weight after <literal>@</literal> allows to adjust the
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probability of drawing the test.
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See below for details.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-j</option> <replaceable>threads</replaceable></term>
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<term><option>--jobs=</option><replaceable>threads</replaceable></term>
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<listitem>
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<para>
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Number of worker threads within <application>pgbench</application>.
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Using more than one thread can be helpful on multi-CPU machines.
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Clients are distributed as evenly as possible among available threads.
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Default is 1.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-l</option></term>
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<term><option>--log</option></term>
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<listitem>
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<para>
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Write information about each transaction to a log file.
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See below for details.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-L</option> <replaceable>limit</replaceable></term>
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<term><option>--latency-limit=</option><replaceable>limit</replaceable></term>
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<listitem>
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<para>
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Transactions that last more than <replaceable>limit</replaceable> milliseconds
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are counted and reported separately, as <firstterm>late</firstterm>.
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</para>
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<para>
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When throttling is used (<option>--rate=...</option>), transactions that
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lag behind schedule by more than <replaceable>limit</replaceable> ms, and thus
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have no hope of meeting the latency limit, are not sent to the server
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at all. They are counted and reported separately as
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<firstterm>skipped</firstterm>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-M</option> <replaceable>querymode</replaceable></term>
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<term><option>--protocol=</option><replaceable>querymode</replaceable></term>
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<listitem>
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<para>
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Protocol to use for submitting queries to the server:
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<itemizedlist>
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<listitem>
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<para><literal>simple</literal>: use simple query protocol.</para>
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</listitem>
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<listitem>
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<para><literal>extended</literal>: use extended query protocol.</para>
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</listitem>
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<listitem>
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<para><literal>prepared</literal>: use extended query protocol with prepared statements.</para>
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</listitem>
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</itemizedlist>
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In the <literal>prepared</literal> mode, <application>pgbench</application>
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reuses the parse analysis result starting from the second query
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iteration, so <application>pgbench</application> runs faster
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than in other modes.
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</para>
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<para>
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The default is simple query protocol. (See <xref linkend="protocol"/>
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for more information.)
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-n</option></term>
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<term><option>--no-vacuum</option></term>
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<listitem>
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<para>
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Perform no vacuuming before running the test.
|
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This option is <emphasis>necessary</emphasis>
|
|
if you are running a custom test scenario that does not include
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the standard tables <structname>pgbench_accounts</structname>,
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<structname>pgbench_branches</structname>, <structname>pgbench_history</structname>, and
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<structname>pgbench_tellers</structname>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-N</option></term>
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<term><option>--skip-some-updates</option></term>
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<listitem>
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<para>
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Run built-in simple-update script.
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Shorthand for <option>-b simple-update</option>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-P</option> <replaceable>sec</replaceable></term>
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<term><option>--progress=</option><replaceable>sec</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
Show progress report every <replaceable>sec</replaceable> seconds. The report
|
|
includes the time since the beginning of the run, the TPS since the
|
|
last report, and the transaction latency average and standard
|
|
deviation since the last report. Under throttling (<option>-R</option>),
|
|
the latency is computed with respect to the transaction scheduled
|
|
start time, not the actual transaction beginning time, thus it also
|
|
includes the average schedule lag time.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>-r</option></term>
|
|
<term><option>--report-latencies</option></term>
|
|
<listitem>
|
|
<para>
|
|
Report the average per-statement latency (execution time from the
|
|
perspective of the client) of each command after the benchmark
|
|
finishes. See below for details.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>-R</option> <replaceable>rate</replaceable></term>
|
|
<term><option>--rate=</option><replaceable>rate</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
Execute transactions targeting the specified rate instead of running
|
|
as fast as possible (the default). The rate is given in transactions
|
|
per second. If the targeted rate is above the maximum possible rate,
|
|
the rate limit won't impact the results.
|
|
</para>
|
|
<para>
|
|
The rate is targeted by starting transactions along a
|
|
Poisson-distributed schedule time line. The expected start time
|
|
schedule moves forward based on when the client first started, not
|
|
when the previous transaction ended. That approach means that when
|
|
transactions go past their original scheduled end time, it is
|
|
possible for later ones to catch up again.
|
|
</para>
|
|
<para>
|
|
When throttling is active, the transaction latency reported at the
|
|
end of the run is calculated from the scheduled start times, so it
|
|
includes the time each transaction had to wait for the previous
|
|
transaction to finish. The wait time is called the schedule lag time,
|
|
and its average and maximum are also reported separately. The
|
|
transaction latency with respect to the actual transaction start time,
|
|
i.e. the time spent executing the transaction in the database, can be
|
|
computed by subtracting the schedule lag time from the reported
|
|
latency.
|
|
</para>
|
|
|
|
<para>
|
|
If <option>--latency-limit</option> is used together with <option>--rate</option>,
|
|
a transaction can lag behind so much that it is already over the
|
|
latency limit when the previous transaction ends, because the latency
|
|
is calculated from the scheduled start time. Such transactions are
|
|
not sent to the server, but are skipped altogether and counted
|
|
separately.
|
|
</para>
|
|
|
|
<para>
|
|
A high schedule lag time is an indication that the system cannot
|
|
process transactions at the specified rate, with the chosen number of
|
|
clients and threads. When the average transaction execution time is
|
|
longer than the scheduled interval between each transaction, each
|
|
successive transaction will fall further behind, and the schedule lag
|
|
time will keep increasing the longer the test run is. When that
|
|
happens, you will have to reduce the specified transaction rate.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>-s</option> <replaceable>scale_factor</replaceable></term>
|
|
<term><option>--scale=</option><replaceable>scale_factor</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
Report the specified scale factor in <application>pgbench</application>'s
|
|
output. With the built-in tests, this is not necessary; the
|
|
correct scale factor will be detected by counting the number of
|
|
rows in the <structname>pgbench_branches</structname> table.
|
|
However, when testing only custom benchmarks (<option>-f</option> option),
|
|
the scale factor will be reported as 1 unless this option is used.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>-S</option></term>
|
|
<term><option>--select-only</option></term>
|
|
<listitem>
|
|
<para>
|
|
Run built-in select-only script.
|
|
Shorthand for <option>-b select-only</option>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>--show-script</option><replaceable>scriptname</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
Show the actual code of builtin script <replaceable>scriptname</replaceable>
|
|
on stderr, and exit immediately.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>-t</option> <replaceable>transactions</replaceable></term>
|
|
<term><option>--transactions=</option><replaceable>transactions</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
Number of transactions each client runs. Default is 10.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>-T</option> <replaceable>seconds</replaceable></term>
|
|
<term><option>--time=</option><replaceable>seconds</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
Run the test for this many seconds, rather than a fixed number of
|
|
transactions per client. <option>-t</option> and
|
|
<option>-T</option> are mutually exclusive.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>-v</option></term>
|
|
<term><option>--vacuum-all</option></term>
|
|
<listitem>
|
|
<para>
|
|
Vacuum all four standard tables before running the test.
|
|
With neither <option>-n</option> nor <option>-v</option>, <application>pgbench</application> will vacuum the
|
|
<structname>pgbench_tellers</structname> and <structname>pgbench_branches</structname>
|
|
tables, and will truncate <structname>pgbench_history</structname>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>--aggregate-interval=<replaceable>seconds</replaceable></option></term>
|
|
<listitem>
|
|
<para>
|
|
Length of aggregation interval (in seconds). May be used only
|
|
with <option>-l</option> option. With this option, the log contains
|
|
per-interval summary data, as described below.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>--log-prefix=<replaceable>prefix</replaceable></option></term>
|
|
<listitem>
|
|
<para>
|
|
Set the filename prefix for the log files created by
|
|
<option>--log</option>. The default is <literal>pgbench_log</literal>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>--progress-timestamp</option></term>
|
|
<listitem>
|
|
<para>
|
|
When showing progress (option <option>-P</option>), use a timestamp
|
|
(Unix epoch) instead of the number of seconds since the
|
|
beginning of the run. The unit is in seconds, with millisecond
|
|
precision after the dot.
|
|
This helps compare logs generated by various tools.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>--random-seed=</option><replaceable>SEED</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
Set random generator seed. Seeds the system random number generator,
|
|
which then produces a sequence of initial generator states, one for
|
|
each thread.
|
|
Values for <replaceable>SEED</replaceable> may be:
|
|
<literal>time</literal> (the default, the seed is based on the current time),
|
|
<literal>rand</literal> (use a strong random source, failing if none
|
|
is available), or an unsigned decimal integer value.
|
|
The random generator is invoked explicitly from a pgbench script
|
|
(<literal>random...</literal> functions) or implicitly (for instance option
|
|
<option>--rate</option> uses it to schedule transactions).
|
|
When explicitly set, the value used for seeding is shown on the terminal.
|
|
Any value allowed for <replaceable>SEED</replaceable> may also be
|
|
provided through the environment variable
|
|
<literal>PGBENCH_RANDOM_SEED</literal>.
|
|
To ensure that the provided seed impacts all possible uses, put this option
|
|
first or use the environment variable.
|
|
</para>
|
|
<para>
|
|
Setting the seed explicitly allows to reproduce a <command>pgbench</command>
|
|
run exactly, as far as random numbers are concerned.
|
|
As the random state is managed per thread, this means the exact same
|
|
<command>pgbench</command> run for an identical invocation if there is one
|
|
client per thread and there are no external or data dependencies.
|
|
From a statistical viewpoint reproducing runs exactly is a bad idea because
|
|
it can hide the performance variability or improve performance unduly,
|
|
e.g. by hitting the same pages as a previous run.
|
|
However, it may also be of great help for debugging, for instance
|
|
re-running a tricky case which leads to an error.
|
|
Use wisely.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>--sampling-rate=<replaceable>rate</replaceable></option></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>
|
|
|
|
</variablelist>
|
|
</para>
|
|
|
|
</refsect2>
|
|
|
|
<refsect2 id="pgbench-common-options">
|
|
<title>Common Options</title>
|
|
|
|
<para>
|
|
<application>pgbench</application> accepts the following command-line
|
|
common arguments:
|
|
|
|
<variablelist>
|
|
|
|
<varlistentry>
|
|
<term><option>-h</option> <replaceable>hostname</replaceable></term>
|
|
<term><option>--host=</option><replaceable>hostname</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
The database server's host name
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>-p</option> <replaceable>port</replaceable></term>
|
|
<term><option>--port=</option><replaceable>port</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
The database server's port number
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>-U</option> <replaceable>login</replaceable></term>
|
|
<term><option>--username=</option><replaceable>login</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
The user name to connect as
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>-V</option></term>
|
|
<term><option>--version</option></term>
|
|
<listitem>
|
|
<para>
|
|
Print the <application>pgbench</application> version and exit.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>-?</option></term>
|
|
<term><option>--help</option></term>
|
|
<listitem>
|
|
<para>
|
|
Show help about <application>pgbench</application> command line
|
|
arguments, and exit.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
|
|
</refsect2>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Exit Status</title>
|
|
|
|
<para>
|
|
A successful run will exit with status 0. Exit status 1 indicates static
|
|
problems such as invalid command-line options. Errors during the run such
|
|
as database errors or problems in the script will result in exit status 2.
|
|
In the latter case, <application>pgbench</application> will print partial
|
|
results.
|
|
</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Notes</title>
|
|
|
|
<refsect2>
|
|
<title>What is the <quote>Transaction</quote> Actually Performed in <application>pgbench</application>?</title>
|
|
|
|
<para>
|
|
<application>pgbench</application> executes test scripts chosen randomly
|
|
from a specified list.
|
|
They include built-in scripts with <option>-b</option> and
|
|
user-provided custom scripts with <option>-f</option>.
|
|
Each script may be given a relative weight specified after a
|
|
<literal>@</literal> so as to change its drawing probability.
|
|
The default weight is <literal>1</literal>.
|
|
Scripts with a weight of <literal>0</literal> are ignored.
|
|
</para>
|
|
|
|
<para>
|
|
The default built-in transaction script (also invoked with <option>-b tpcb-like</option>)
|
|
issues seven commands per transaction over randomly chosen <literal>aid</literal>,
|
|
<literal>tid</literal>, <literal>bid</literal> and <literal>delta</literal>.
|
|
The scenario is inspired by the TPC-B benchmark, but is not actually TPC-B,
|
|
hence the name.
|
|
</para>
|
|
|
|
<orderedlist>
|
|
<listitem><para><literal>BEGIN;</literal></para></listitem>
|
|
<listitem><para><literal>UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;</literal></para></listitem>
|
|
<listitem><para><literal>SELECT abalance FROM pgbench_accounts WHERE aid = :aid;</literal></para></listitem>
|
|
<listitem><para><literal>UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;</literal></para></listitem>
|
|
<listitem><para><literal>UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;</literal></para></listitem>
|
|
<listitem><para><literal>INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);</literal></para></listitem>
|
|
<listitem><para><literal>END;</literal></para></listitem>
|
|
</orderedlist>
|
|
|
|
<para>
|
|
If you select the <literal>simple-update</literal> built-in (also <option>-N</option>),
|
|
steps 4 and 5 aren't included in the transaction.
|
|
This will avoid update contention on these tables, but
|
|
it makes the test case even less like TPC-B.
|
|
</para>
|
|
|
|
<para>
|
|
If you select the <literal>select-only</literal> built-in (also <option>-S</option>),
|
|
only the <command>SELECT</command> is issued.
|
|
</para>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Custom Scripts</title>
|
|
|
|
<para>
|
|
<application>pgbench</application> has support for running custom
|
|
benchmark scenarios by replacing the default transaction script
|
|
(described above) with a transaction script read from a file
|
|
(<option>-f</option> option). In this case a <quote>transaction</quote>
|
|
counts as one execution of a script file.
|
|
</para>
|
|
|
|
<para>
|
|
A script file contains one or more SQL commands terminated by
|
|
semicolons. Empty lines and lines beginning with
|
|
<literal>--</literal> are ignored. Script files can also contain
|
|
<quote>meta commands</quote>, which are interpreted by <application>pgbench</application>
|
|
itself, as described below.
|
|
</para>
|
|
|
|
<note>
|
|
<para>
|
|
Before <productname>PostgreSQL</productname> 9.6, SQL commands in script files
|
|
were terminated by newlines, and so they could not be continued across
|
|
lines. Now a semicolon is <emphasis>required</emphasis> to separate consecutive
|
|
SQL commands (though a SQL command does not need one if it is followed
|
|
by a meta command). If you need to create a script file that works with
|
|
both old and new versions of <application>pgbench</application>, be sure to write
|
|
each SQL command on a single line ending with a semicolon.
|
|
</para>
|
|
</note>
|
|
|
|
<para>
|
|
There is a simple variable-substitution facility for script files.
|
|
Variable names must consist of letters (including non-Latin letters),
|
|
digits, and underscores.
|
|
Variables can be set by the command-line <option>-D</option> option,
|
|
explained above, or by the meta commands explained below.
|
|
In addition to any variables preset by <option>-D</option> command-line options,
|
|
there are a few variables that are preset automatically, listed in
|
|
<xref linkend="pgbench-automatic-variables"/>. A value specified for these
|
|
variables using <option>-D</option> takes precedence over the automatic presets.
|
|
Once set, a variable's
|
|
value can be inserted into a SQL command by writing
|
|
<literal>:</literal><replaceable>variablename</replaceable>. When running more than
|
|
one client session, each session has its own set of variables.
|
|
<application>pgbench</application> supports up to 255 variable uses in one
|
|
statement.
|
|
</para>
|
|
|
|
<table id="pgbench-automatic-variables">
|
|
<title>Automatic Variables</title>
|
|
<tgroup cols="2">
|
|
<thead>
|
|
<row>
|
|
<entry>Variable</entry>
|
|
<entry>Description</entry>
|
|
</row>
|
|
</thead>
|
|
|
|
<tbody>
|
|
<row>
|
|
<entry> <literal>client_id</literal> </entry>
|
|
<entry>unique number identifying the client session (starts from zero)</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry> <literal>default_seed</literal> </entry>
|
|
<entry>seed used in hash functions by default</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry> <literal>random_seed</literal> </entry>
|
|
<entry>random generator seed (unless overwritten with <option>-D</option>)</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry> <literal>scale</literal> </entry>
|
|
<entry>current scale factor</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<para>
|
|
Script file meta commands begin with a backslash (<literal>\</literal>) and
|
|
normally extend to the end of the line, although they can be continued
|
|
to additional lines by writing backslash-return.
|
|
Arguments to a meta command are separated by white space.
|
|
These meta commands are supported:
|
|
</para>
|
|
|
|
<variablelist>
|
|
<varlistentry id='pgbench-metacommand-gset'>
|
|
<term>
|
|
<literal>\gset [<replaceable>prefix</replaceable>]</literal>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
This command may be used to end SQL queries, taking the place of the
|
|
terminating semicolon (<literal>;</literal>).
|
|
</para>
|
|
|
|
<para>
|
|
When this command is used, the preceding SQL query is expected to
|
|
return one row, the columns of which are stored into variables named after
|
|
column names, and prefixed with <replaceable>prefix</replaceable> if provided.
|
|
</para>
|
|
|
|
<para>
|
|
The following example puts the final account balance from the first query
|
|
into variable <replaceable>abalance</replaceable>, and fills variables
|
|
<replaceable>p_two</replaceable> and <replaceable>p_three</replaceable>
|
|
with integers from the third query.
|
|
The result of the second query is discarded.
|
|
<programlisting>
|
|
UPDATE pgbench_accounts
|
|
SET abalance = abalance + :delta
|
|
WHERE aid = :aid
|
|
RETURNING abalance \gset
|
|
-- compound of two queries
|
|
SELECT 1 \;
|
|
SELECT 2 AS two, 3 AS three \gset p_
|
|
</programlisting>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><literal>\if</literal> <replaceable class="parameter">expression</replaceable></term>
|
|
<term><literal>\elif</literal> <replaceable class="parameter">expression</replaceable></term>
|
|
<term><literal>\else</literal></term>
|
|
<term><literal>\endif</literal></term>
|
|
<listitem>
|
|
<para>
|
|
This group of commands implements nestable conditional blocks,
|
|
similarly to <literal>psql</literal>'s <xref linkend="psql-metacommand-if"/>.
|
|
Conditional expressions are identical to those with <literal>\set</literal>,
|
|
with non-zero values interpreted as true.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry id='pgbench-metacommand-set'>
|
|
<term>
|
|
<literal>\set <replaceable>varname</replaceable> <replaceable>expression</replaceable></literal>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
Sets variable <replaceable>varname</replaceable> to a value calculated
|
|
from <replaceable>expression</replaceable>.
|
|
The expression may contain the <literal>NULL</literal> constant,
|
|
Boolean constants <literal>TRUE</literal> and <literal>FALSE</literal>,
|
|
integer constants such as <literal>5432</literal>,
|
|
double constants such as <literal>3.14159</literal>,
|
|
references to variables <literal>:</literal><replaceable>variablename</replaceable>,
|
|
<link linkend="pgbench-builtin-operators">operators</link>
|
|
with their usual SQL precedence and associativity,
|
|
<link linkend="pgbench-builtin-functions">function calls</link>,
|
|
SQL <link linkend="functions-case"><token>CASE</token> generic conditional
|
|
expressions</link> and parentheses.
|
|
</para>
|
|
|
|
<para>
|
|
Functions and most operators return <literal>NULL</literal> on
|
|
<literal>NULL</literal> input.
|
|
</para>
|
|
|
|
<para>
|
|
For conditional purposes, non zero numerical values are
|
|
<literal>TRUE</literal>, zero numerical values and <literal>NULL</literal>
|
|
are <literal>FALSE</literal>.
|
|
</para>
|
|
|
|
<para>
|
|
Too large or small integer and double constants, as well as
|
|
integer arithmetic operators (<literal>+</literal>,
|
|
<literal>-</literal>, <literal>*</literal> and <literal>/</literal>)
|
|
raise errors on overflows.
|
|
</para>
|
|
|
|
<para>
|
|
When no final <token>ELSE</token> clause is provided to a
|
|
<token>CASE</token>, the default value is <literal>NULL</literal>.
|
|
</para>
|
|
|
|
<para>
|
|
Examples:
|
|
<programlisting>
|
|
\set ntellers 10 * :scale
|
|
\set aid (1021 * random(1, 100000 * :scale)) % \
|
|
(100000 * :scale) + 1
|
|
\set divx CASE WHEN :x <> 0 THEN :y/:x ELSE NULL END
|
|
</programlisting></para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal>\sleep <replaceable>number</replaceable> [ us | ms | s ]</literal>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
Causes script execution to sleep for the specified duration in
|
|
microseconds (<literal>us</literal>), milliseconds (<literal>ms</literal>) or seconds
|
|
(<literal>s</literal>). If the unit is omitted then seconds are the default.
|
|
<replaceable>number</replaceable> can be either an integer constant or a
|
|
<literal>:</literal><replaceable>variablename</replaceable> reference to a variable
|
|
having an integer value.
|
|
</para>
|
|
|
|
<para>
|
|
Example:
|
|
<programlisting>
|
|
\sleep 10 ms
|
|
</programlisting></para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal>\setshell <replaceable>varname</replaceable> <replaceable>command</replaceable> [ <replaceable>argument</replaceable> ... ]</literal>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
Sets variable <replaceable>varname</replaceable> to the result of the shell command
|
|
<replaceable>command</replaceable> with the given <replaceable>argument</replaceable>(s).
|
|
The command must return an integer value through its standard output.
|
|
</para>
|
|
|
|
<para>
|
|
<replaceable>command</replaceable> and each <replaceable>argument</replaceable> can be either
|
|
a text constant or a <literal>:</literal><replaceable>variablename</replaceable> reference
|
|
to a variable. If you want to use an <replaceable>argument</replaceable> starting
|
|
with a colon, write an additional colon at the beginning of
|
|
<replaceable>argument</replaceable>.
|
|
</para>
|
|
|
|
<para>
|
|
Example:
|
|
<programlisting>
|
|
\setshell variable_to_be_assigned command literal_argument :variable ::literal_starting_with_colon
|
|
</programlisting></para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>
|
|
<literal>\shell <replaceable>command</replaceable> [ <replaceable>argument</replaceable> ... ]</literal>
|
|
</term>
|
|
|
|
<listitem>
|
|
<para>
|
|
Same as <literal>\setshell</literal>, but the result of the command
|
|
is discarded.
|
|
</para>
|
|
|
|
<para>
|
|
Example:
|
|
<programlisting>
|
|
\shell command literal_argument :variable ::literal_starting_with_colon
|
|
</programlisting></para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</refsect2>
|
|
|
|
<refsect2 id="pgbench-builtin-operators">
|
|
<title>Built-In Operators</title>
|
|
|
|
<para>
|
|
The arithmetic, bitwise, comparison and logical operators listed in
|
|
<xref linkend="pgbench-operators"/> are built into <application>pgbench</application>
|
|
and may be used in expressions appearing in
|
|
<link linkend="pgbench-metacommand-set"><literal>\set</literal></link>.
|
|
</para>
|
|
|
|
<table id="pgbench-operators">
|
|
<title>pgbench Operators by increasing precedence</title>
|
|
<tgroup cols="4">
|
|
<thead>
|
|
<row>
|
|
<entry>Operator</entry>
|
|
<entry>Description</entry>
|
|
<entry>Example</entry>
|
|
<entry>Result</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody>
|
|
<row>
|
|
<entry><literal>OR</literal></entry>
|
|
<entry>logical or</entry>
|
|
<entry><literal>5 or 0</literal></entry>
|
|
<entry><literal>TRUE</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>AND</literal></entry>
|
|
<entry>logical and</entry>
|
|
<entry><literal>3 and 0</literal></entry>
|
|
<entry><literal>FALSE</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>NOT</literal></entry>
|
|
<entry>logical not</entry>
|
|
<entry><literal>not false</literal></entry>
|
|
<entry><literal>TRUE</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>IS [NOT] (NULL|TRUE|FALSE)</literal></entry>
|
|
<entry>value tests</entry>
|
|
<entry><literal>1 is null</literal></entry>
|
|
<entry><literal>FALSE</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>ISNULL|NOTNULL</literal></entry>
|
|
<entry>null tests</entry>
|
|
<entry><literal>1 notnull</literal></entry>
|
|
<entry><literal>TRUE</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>=</literal></entry>
|
|
<entry>is equal</entry>
|
|
<entry><literal>5 = 4</literal></entry>
|
|
<entry><literal>FALSE</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><></literal></entry>
|
|
<entry>is not equal</entry>
|
|
<entry><literal>5 <> 4</literal></entry>
|
|
<entry><literal>TRUE</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>!=</literal></entry>
|
|
<entry>is not equal</entry>
|
|
<entry><literal>5 != 5</literal></entry>
|
|
<entry><literal>FALSE</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><</literal></entry>
|
|
<entry>lower than</entry>
|
|
<entry><literal>5 < 4</literal></entry>
|
|
<entry><literal>FALSE</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><=</literal></entry>
|
|
<entry>lower or equal</entry>
|
|
<entry><literal>5 <= 4</literal></entry>
|
|
<entry><literal>FALSE</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>></literal></entry>
|
|
<entry>greater than</entry>
|
|
<entry><literal>5 > 4</literal></entry>
|
|
<entry><literal>TRUE</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>>=</literal></entry>
|
|
<entry>greater or equal</entry>
|
|
<entry><literal>5 >= 4</literal></entry>
|
|
<entry><literal>TRUE</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>|</literal></entry>
|
|
<entry>integer bitwise OR</entry>
|
|
<entry><literal>1 | 2</literal></entry>
|
|
<entry><literal>3</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>#</literal></entry>
|
|
<entry>integer bitwise XOR</entry>
|
|
<entry><literal>1 # 3</literal></entry>
|
|
<entry><literal>2</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>&</literal></entry>
|
|
<entry>integer bitwise AND</entry>
|
|
<entry><literal>1 & 3</literal></entry>
|
|
<entry><literal>1</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>~</literal></entry>
|
|
<entry>integer bitwise NOT</entry>
|
|
<entry><literal>~ 1</literal></entry>
|
|
<entry><literal>-2</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><<</literal></entry>
|
|
<entry>integer bitwise shift left</entry>
|
|
<entry><literal>1 << 2</literal></entry>
|
|
<entry><literal>4</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>>></literal></entry>
|
|
<entry>integer bitwise shift right</entry>
|
|
<entry><literal>8 >> 2</literal></entry>
|
|
<entry><literal>2</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>+</literal></entry>
|
|
<entry>addition</entry>
|
|
<entry><literal>5 + 4</literal></entry>
|
|
<entry><literal>9</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>-</literal></entry>
|
|
<entry>subtraction</entry>
|
|
<entry><literal>3 - 2.0</literal></entry>
|
|
<entry><literal>1.0</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>*</literal></entry>
|
|
<entry>multiplication</entry>
|
|
<entry><literal>5 * 4</literal></entry>
|
|
<entry><literal>20</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>/</literal></entry>
|
|
<entry>division (integer truncates the results)</entry>
|
|
<entry><literal>5 / 3</literal></entry>
|
|
<entry><literal>1</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>%</literal></entry>
|
|
<entry>modulo</entry>
|
|
<entry><literal>3 % 2</literal></entry>
|
|
<entry><literal>1</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal>-</literal></entry>
|
|
<entry>opposite</entry>
|
|
<entry><literal>- 2.0</literal></entry>
|
|
<entry><literal>-2.0</literal></entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</refsect2>
|
|
|
|
<refsect2 id="pgbench-builtin-functions">
|
|
<title>Built-In Functions</title>
|
|
|
|
<para>
|
|
The functions listed in <xref linkend="pgbench-functions"/> are built
|
|
into <application>pgbench</application> and may be used in expressions appearing in
|
|
<link linkend="pgbench-metacommand-set"><literal>\set</literal></link>.
|
|
</para>
|
|
|
|
<!-- list pgbench functions in alphabetical order -->
|
|
<table id="pgbench-functions">
|
|
<title>pgbench Functions</title>
|
|
<tgroup cols="5">
|
|
<thead>
|
|
<row>
|
|
<entry>Function</entry>
|
|
<entry>Return Type</entry>
|
|
<entry>Description</entry>
|
|
<entry>Example</entry>
|
|
<entry>Result</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody>
|
|
<row>
|
|
<entry><literal><function>abs(<replaceable>a</replaceable>)</function></literal></entry>
|
|
<entry>same as <replaceable>a</replaceable></entry>
|
|
<entry>absolute value</entry>
|
|
<entry><literal>abs(-17)</literal></entry>
|
|
<entry><literal>17</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>debug(<replaceable>a</replaceable>)</function></literal></entry>
|
|
<entry>same as <replaceable>a</replaceable> </entry>
|
|
<entry>print <replaceable>a</replaceable> to <systemitem>stderr</systemitem>,
|
|
and return <replaceable>a</replaceable></entry>
|
|
<entry><literal>debug(5432.1)</literal></entry>
|
|
<entry><literal>5432.1</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>double(<replaceable>i</replaceable>)</function></literal></entry>
|
|
<entry>double</entry>
|
|
<entry>cast to double</entry>
|
|
<entry><literal>double(5432)</literal></entry>
|
|
<entry><literal>5432.0</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>exp(<replaceable>x</replaceable>)</function></literal></entry>
|
|
<entry>double</entry>
|
|
<entry>exponential</entry>
|
|
<entry><literal>exp(1.0)</literal></entry>
|
|
<entry><literal>2.718281828459045</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>greatest(<replaceable>a</replaceable> [, <replaceable>...</replaceable> ] )</function></literal></entry>
|
|
<entry>double if any <replaceable>a</replaceable> is double, else integer</entry>
|
|
<entry>largest value among arguments</entry>
|
|
<entry><literal>greatest(5, 4, 3, 2)</literal></entry>
|
|
<entry><literal>5</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>hash(<replaceable>a</replaceable> [, <replaceable>seed</replaceable> ] )</function></literal></entry>
|
|
<entry>integer</entry>
|
|
<entry>alias for <literal>hash_murmur2()</literal></entry>
|
|
<entry><literal>hash(10, 5432)</literal></entry>
|
|
<entry><literal>-5817877081768721676</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>hash_fnv1a(<replaceable>a</replaceable> [, <replaceable>seed</replaceable> ] )</function></literal></entry>
|
|
<entry>integer</entry>
|
|
<entry><ulink url="https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function">FNV-1a hash</ulink></entry>
|
|
<entry><literal>hash_fnv1a(10, 5432)</literal></entry>
|
|
<entry><literal>-7793829335365542153</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>hash_murmur2(<replaceable>a</replaceable> [, <replaceable>seed</replaceable> ] )</function></literal></entry>
|
|
<entry>integer</entry>
|
|
<entry><ulink url="https://en.wikipedia.org/wiki/MurmurHash">MurmurHash2 hash</ulink></entry>
|
|
<entry><literal>hash_murmur2(10, 5432)</literal></entry>
|
|
<entry><literal>-5817877081768721676</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>int(<replaceable>x</replaceable>)</function></literal></entry>
|
|
<entry>integer</entry>
|
|
<entry>cast to int</entry>
|
|
<entry><literal>int(5.4 + 3.8)</literal></entry>
|
|
<entry><literal>9</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>least(<replaceable>a</replaceable> [, <replaceable>...</replaceable> ] )</function></literal></entry>
|
|
<entry>double if any <replaceable>a</replaceable> is double, else integer</entry>
|
|
<entry>smallest value among arguments</entry>
|
|
<entry><literal>least(5, 4, 3, 2.1)</literal></entry>
|
|
<entry><literal>2.1</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>ln(<replaceable>x</replaceable>)</function></literal></entry>
|
|
<entry>double</entry>
|
|
<entry>natural logarithm</entry>
|
|
<entry><literal>ln(2.718281828459045)</literal></entry>
|
|
<entry><literal>1.0</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>mod(<replaceable>i</replaceable>, <replaceable>j</replaceable>)</function></literal></entry>
|
|
<entry>integer</entry>
|
|
<entry>modulo</entry>
|
|
<entry><literal>mod(54, 32)</literal></entry>
|
|
<entry><literal>22</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>pi()</function></literal></entry>
|
|
<entry>double</entry>
|
|
<entry>value of the constant PI</entry>
|
|
<entry><literal>pi()</literal></entry>
|
|
<entry><literal>3.14159265358979323846</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>pow(<replaceable>x</replaceable>, <replaceable>y</replaceable>)</function>, <function>power(<replaceable>x</replaceable>, <replaceable>y</replaceable>)</function></literal></entry>
|
|
<entry>double</entry>
|
|
<entry>exponentiation</entry>
|
|
<entry><literal>pow(2.0, 10)</literal>, <literal>power(2.0, 10)</literal></entry>
|
|
<entry><literal>1024.0</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>random(<replaceable>lb</replaceable>, <replaceable>ub</replaceable>)</function></literal></entry>
|
|
<entry>integer</entry>
|
|
<entry>uniformly-distributed random integer in <literal>[lb, ub]</literal></entry>
|
|
<entry><literal>random(1, 10)</literal></entry>
|
|
<entry>an integer between <literal>1</literal> and <literal>10</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>random_exponential(<replaceable>lb</replaceable>, <replaceable>ub</replaceable>, <replaceable>parameter</replaceable>)</function></literal></entry>
|
|
<entry>integer</entry>
|
|
<entry>exponentially-distributed random integer in <literal>[lb, ub]</literal>,
|
|
see below</entry>
|
|
<entry><literal>random_exponential(1, 10, 3.0)</literal></entry>
|
|
<entry>an integer between <literal>1</literal> and <literal>10</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>random_gaussian(<replaceable>lb</replaceable>, <replaceable>ub</replaceable>, <replaceable>parameter</replaceable>)</function></literal></entry>
|
|
<entry>integer</entry>
|
|
<entry>Gaussian-distributed random integer in <literal>[lb, ub]</literal>,
|
|
see below</entry>
|
|
<entry><literal>random_gaussian(1, 10, 2.5)</literal></entry>
|
|
<entry>an integer between <literal>1</literal> and <literal>10</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>random_zipfian(<replaceable>lb</replaceable>, <replaceable>ub</replaceable>, <replaceable>parameter</replaceable>)</function></literal></entry>
|
|
<entry>integer</entry>
|
|
<entry>Zipfian-distributed random integer in <literal>[lb, ub]</literal>,
|
|
see below</entry>
|
|
<entry><literal>random_zipfian(1, 10, 1.5)</literal></entry>
|
|
<entry>an integer between <literal>1</literal> and <literal>10</literal></entry>
|
|
</row>
|
|
<row>
|
|
<entry><literal><function>sqrt(<replaceable>x</replaceable>)</function></literal></entry>
|
|
<entry>double</entry>
|
|
<entry>square root</entry>
|
|
<entry><literal>sqrt(2.0)</literal></entry>
|
|
<entry><literal>1.414213562</literal></entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<para>
|
|
The <literal>random</literal> function generates values using a uniform
|
|
distribution, that is all the values are drawn within the specified
|
|
range with equal probability. The <literal>random_exponential</literal>,
|
|
<literal>random_gaussian</literal> and <literal>random_zipfian</literal>
|
|
functions require an additional double parameter which determines the precise
|
|
shape of the distribution.
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
For an exponential distribution, <replaceable>parameter</replaceable>
|
|
controls the distribution by truncating a quickly-decreasing
|
|
exponential distribution at <replaceable>parameter</replaceable>, and then
|
|
projecting onto integers between the bounds.
|
|
To be precise, with
|
|
<literallayout>
|
|
f(x) = exp(-parameter * (x - min) / (max - min + 1)) / (1 - exp(-parameter))
|
|
</literallayout>
|
|
Then value <replaceable>i</replaceable> between <replaceable>min</replaceable> and
|
|
<replaceable>max</replaceable> inclusive is drawn with probability:
|
|
<literal>f(i) - f(i + 1)</literal>.
|
|
</para>
|
|
|
|
<para>
|
|
Intuitively, the larger the <replaceable>parameter</replaceable>, the more
|
|
frequently values close to <replaceable>min</replaceable> are accessed, and the
|
|
less frequently values close to <replaceable>max</replaceable> are accessed.
|
|
The closer to 0 <replaceable>parameter</replaceable> is, the flatter (more
|
|
uniform) the access distribution.
|
|
A crude approximation of the distribution is that the most frequent 1%
|
|
values in the range, close to <replaceable>min</replaceable>, are drawn
|
|
<replaceable>parameter</replaceable>% of the time.
|
|
The <replaceable>parameter</replaceable> value must be strictly positive.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
For a Gaussian distribution, the interval is mapped onto a standard
|
|
normal distribution (the classical bell-shaped Gaussian curve) truncated
|
|
at <literal>-parameter</literal> on the left and <literal>+parameter</literal>
|
|
on the right.
|
|
Values in the middle of the interval are more likely to be drawn.
|
|
To be precise, if <literal>PHI(x)</literal> is the cumulative distribution
|
|
function of the standard normal distribution, with mean <literal>mu</literal>
|
|
defined as <literal>(max + min) / 2.0</literal>, with
|
|
<literallayout>
|
|
f(x) = PHI(2.0 * parameter * (x - mu) / (max - min + 1)) /
|
|
(2.0 * PHI(parameter) - 1)
|
|
</literallayout>
|
|
then value <replaceable>i</replaceable> between <replaceable>min</replaceable> and
|
|
<replaceable>max</replaceable> inclusive is drawn with probability:
|
|
<literal>f(i + 0.5) - f(i - 0.5)</literal>.
|
|
Intuitively, the larger the <replaceable>parameter</replaceable>, the more
|
|
frequently values close to the middle of the interval are drawn, and the
|
|
less frequently values close to the <replaceable>min</replaceable> and
|
|
<replaceable>max</replaceable> bounds. About 67% of values are drawn from the
|
|
middle <literal>1.0 / parameter</literal>, that is a relative
|
|
<literal>0.5 / parameter</literal> around the mean, and 95% in the middle
|
|
<literal>2.0 / parameter</literal>, that is a relative
|
|
<literal>1.0 / parameter</literal> around the mean; for instance, if
|
|
<replaceable>parameter</replaceable> is 4.0, 67% of values are drawn from the
|
|
middle quarter (1.0 / 4.0) of the interval (i.e. from
|
|
<literal>3.0 / 8.0</literal> to <literal>5.0 / 8.0</literal>) and 95% from
|
|
the middle half (<literal>2.0 / 4.0</literal>) of the interval (second and third
|
|
quartiles). The minimum allowed <replaceable>parameter</replaceable>
|
|
value is 2.0.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
<literal>random_zipfian</literal> generates a bounded Zipfian
|
|
distribution.
|
|
<replaceable>parameter</replaceable> defines how skewed the distribution
|
|
is. The larger the <replaceable>parameter</replaceable>, the more
|
|
frequently values closer to the beginning of the interval are drawn.
|
|
The distribution is such that, assuming the range starts from 1,
|
|
the ratio of the probability of drawing <replaceable>k</replaceable>
|
|
versus drawing <replaceable>k+1</replaceable> is
|
|
<literal>((<replaceable>k</replaceable>+1)/<replaceable>k</replaceable>)**<replaceable>parameter</replaceable></literal>.
|
|
For example, <literal>random_zipfian(1, ..., 2.5)</literal> produces
|
|
the value <literal>1</literal> about <literal>(2/1)**2.5 =
|
|
5.66</literal> times more frequently than <literal>2</literal>, which
|
|
itself is produced <literal>(3/2)**2.5 = 2.76</literal> times more
|
|
frequently than <literal>3</literal>, and so on.
|
|
</para>
|
|
<para>
|
|
<application>pgbench</application>'s implementation is based on
|
|
"Non-Uniform Random Variate Generation", Luc Devroye, p. 550-551,
|
|
Springer 1986. Due to limitations of that algorithm,
|
|
the <replaceable>parameter</replaceable> value is restricted to
|
|
the range [1.001, 1000].
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>
|
|
Hash functions <literal>hash</literal>, <literal>hash_murmur2</literal> and
|
|
<literal>hash_fnv1a</literal> accept an input value and an optional seed parameter.
|
|
In case the seed isn't provided the value of <literal>:default_seed</literal>
|
|
is used, which is initialized randomly unless set by the command-line
|
|
<literal>-D</literal> option. Hash functions can be used to scatter the
|
|
distribution of random functions such as <literal>random_zipfian</literal> or
|
|
<literal>random_exponential</literal>. For instance, the following pgbench
|
|
script simulates possible real world workload typical for social media and
|
|
blogging platforms where few accounts generate excessive load:
|
|
|
|
<programlisting>
|
|
\set r random_zipfian(0, 100000000, 1.07)
|
|
\set k abs(hash(:r)) % 1000000
|
|
</programlisting>
|
|
|
|
In some cases several distinct distributions are needed which don't correlate
|
|
with each other and this is when implicit seed parameter comes in handy:
|
|
|
|
<programlisting>
|
|
\set k1 abs(hash(:r, :default_seed + 123)) % 1000000
|
|
\set k2 abs(hash(:r, :default_seed + 321)) % 1000000
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
As an example, the full definition of the built-in TPC-B-like
|
|
transaction is:
|
|
|
|
<programlisting>
|
|
\set aid random(1, 100000 * :scale)
|
|
\set bid random(1, 1 * :scale)
|
|
\set tid random(1, 10 * :scale)
|
|
\set delta random(-5000, 5000)
|
|
BEGIN;
|
|
UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;
|
|
SELECT abalance FROM pgbench_accounts WHERE aid = :aid;
|
|
UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;
|
|
UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;
|
|
INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);
|
|
END;
|
|
</programlisting>
|
|
|
|
This script allows each iteration of the transaction to reference
|
|
different, randomly-chosen rows. (This example also shows why it's
|
|
important for each client session to have its own variables —
|
|
otherwise they'd not be independently touching different rows.)
|
|
</para>
|
|
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Per-Transaction Logging</title>
|
|
|
|
<para>
|
|
With the <option>-l</option> option (but without
|
|
the <option>--aggregate-interval</option> option),
|
|
<application>pgbench</application> writes information about each transaction
|
|
to a log file. The log file will be named
|
|
<filename><replaceable>prefix</replaceable>.<replaceable>nnn</replaceable></filename>,
|
|
where <replaceable>prefix</replaceable> defaults to <literal>pgbench_log</literal>, and
|
|
<replaceable>nnn</replaceable> is the PID of the
|
|
<application>pgbench</application> process.
|
|
The prefix can be changed by using the <option>--log-prefix</option> option.
|
|
If the <option>-j</option> option is 2 or higher, so that there are multiple
|
|
worker threads, each will have its own log file. The first worker will
|
|
use the same name for its log file as in the standard single worker case.
|
|
The additional log files for the other workers will be named
|
|
<filename><replaceable>prefix</replaceable>.<replaceable>nnn</replaceable>.<replaceable>mmm</replaceable></filename>,
|
|
where <replaceable>mmm</replaceable> is a sequential number for each worker starting
|
|
with 1.
|
|
</para>
|
|
|
|
<para>
|
|
The format of the log is:
|
|
|
|
<synopsis>
|
|
<replaceable>client_id</replaceable> <replaceable>transaction_no</replaceable> <replaceable>time</replaceable> <replaceable>script_no</replaceable> <replaceable>time_epoch</replaceable> <replaceable>time_us</replaceable> <optional> <replaceable>schedule_lag</replaceable> </optional>
|
|
</synopsis>
|
|
|
|
where
|
|
<replaceable>client_id</replaceable> indicates which client session ran the transaction,
|
|
<replaceable>transaction_no</replaceable> counts how many transactions have been
|
|
run by that session,
|
|
<replaceable>time</replaceable> is the total elapsed transaction time in microseconds,
|
|
<replaceable>script_no</replaceable> identifies which script file was used (useful when
|
|
multiple scripts were specified with <option>-f</option> or <option>-b</option>),
|
|
and <replaceable>time_epoch</replaceable>/<replaceable>time_us</replaceable> are a
|
|
Unix-epoch time stamp and an offset
|
|
in microseconds (suitable for creating an ISO 8601
|
|
time stamp with fractional seconds) showing when
|
|
the transaction completed.
|
|
The <replaceable>schedule_lag</replaceable> field is the difference between the
|
|
transaction's scheduled start time, and the time it actually started, in
|
|
microseconds. It is only present when the <option>--rate</option> option is used.
|
|
When both <option>--rate</option> and <option>--latency-limit</option> are used,
|
|
the <replaceable>time</replaceable> for a skipped transaction will be reported as
|
|
<literal>skipped</literal>.
|
|
</para>
|
|
|
|
<para>
|
|
Here is a snippet of a log file generated in a single-client run:
|
|
<screen>
|
|
0 199 2241 0 1175850568 995598
|
|
0 200 2465 0 1175850568 998079
|
|
0 201 2513 0 1175850569 608
|
|
0 202 2038 0 1175850569 2663
|
|
</screen>
|
|
|
|
Another example with <literal>--rate=100</literal>
|
|
and <literal>--latency-limit=5</literal> (note the additional
|
|
<replaceable>schedule_lag</replaceable> column):
|
|
<screen>
|
|
0 81 4621 0 1412881037 912698 3005
|
|
0 82 6173 0 1412881037 914578 4304
|
|
0 83 skipped 0 1412881037 914578 5217
|
|
0 83 skipped 0 1412881037 914578 5099
|
|
0 83 4722 0 1412881037 916203 3108
|
|
0 84 4142 0 1412881037 918023 2333
|
|
0 85 2465 0 1412881037 919759 740
|
|
</screen>
|
|
In this example, transaction 82 was late, because its latency (6.173 ms) was
|
|
over the 5 ms limit. The next two transactions were skipped, because they
|
|
were already late before they were even started.
|
|
</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> option
|
|
can be used to log only a random sample of transactions.
|
|
</para>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Aggregated Logging</title>
|
|
|
|
<para>
|
|
With the <option>--aggregate-interval</option> option, a different
|
|
format is used for the log files:
|
|
|
|
<synopsis>
|
|
<replaceable>interval_start</replaceable> <replaceable>num_transactions</replaceable> <replaceable>sum_latency</replaceable> <replaceable>sum_latency_2</replaceable> <replaceable>min_latency</replaceable> <replaceable>max_latency</replaceable> <optional> <replaceable>sum_lag</replaceable> <replaceable>sum_lag_2</replaceable> <replaceable>min_lag</replaceable> <replaceable>max_lag</replaceable> <optional> <replaceable>skipped</replaceable> </optional> </optional>
|
|
</synopsis>
|
|
|
|
where
|
|
<replaceable>interval_start</replaceable> is the start of the interval (as a Unix
|
|
epoch time stamp),
|
|
<replaceable>num_transactions</replaceable> is the number of transactions
|
|
within the interval,
|
|
<replaceable>sum_latency</replaceable> is the sum of the transaction
|
|
latencies within the interval,
|
|
<replaceable>sum_latency_2</replaceable> is the sum of squares of the
|
|
transaction latencies within the interval,
|
|
<replaceable>min_latency</replaceable> is the minimum latency within the interval,
|
|
and
|
|
<replaceable>max_latency</replaceable> is the maximum latency within the interval.
|
|
The next fields,
|
|
<replaceable>sum_lag</replaceable>, <replaceable>sum_lag_2</replaceable>, <replaceable>min_lag</replaceable>,
|
|
and <replaceable>max_lag</replaceable>, are only present if the <option>--rate</option>
|
|
option is used.
|
|
They provide statistics about the time each transaction had to wait for the
|
|
previous one to finish, i.e. the difference between each transaction's
|
|
scheduled start time and the time it actually started.
|
|
The very last field, <replaceable>skipped</replaceable>,
|
|
is only present if the <option>--latency-limit</option> option is used, too.
|
|
It counts the number of transactions skipped because they would have
|
|
started too late.
|
|
Each transaction is counted in the interval when it was committed.
|
|
</para>
|
|
|
|
<para>
|
|
Here is some example output:
|
|
<screen>
|
|
1345828501 5601 1542744 483552416 61 2573
|
|
1345828503 7884 1979812 565806736 60 1479
|
|
1345828505 7208 1979422 567277552 59 1391
|
|
1345828507 7685 1980268 569784714 60 1398
|
|
1345828509 7073 1979779 573489941 236 1411
|
|
</screen></para>
|
|
|
|
<para>
|
|
Notice that while the plain (unaggregated) log file shows which script
|
|
was used for each transaction, the aggregated log does not. Therefore if
|
|
you need per-script data, you need to aggregate the data on your own.
|
|
</para>
|
|
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Per-Statement Latencies</title>
|
|
|
|
<para>
|
|
With the <option>-r</option> option, <application>pgbench</application> collects
|
|
the elapsed transaction time of each statement executed by every
|
|
client. It then reports an average of those values, referred to
|
|
as the latency for each statement, after the benchmark has finished.
|
|
</para>
|
|
|
|
<para>
|
|
For the default script, the output will look similar to this:
|
|
<screen>
|
|
starting vacuum...end.
|
|
transaction type: <builtin: TPC-B (sort of)>
|
|
scaling factor: 1
|
|
query mode: simple
|
|
number of clients: 10
|
|
number of threads: 1
|
|
number of transactions per client: 1000
|
|
number of transactions actually processed: 10000/10000
|
|
latency average = 15.844 ms
|
|
latency stddev = 2.715 ms
|
|
tps = 618.764555 (including connections establishing)
|
|
tps = 622.977698 (excluding connections establishing)
|
|
statement latencies in milliseconds:
|
|
0.002 \set aid random(1, 100000 * :scale)
|
|
0.005 \set bid random(1, 1 * :scale)
|
|
0.002 \set tid random(1, 10 * :scale)
|
|
0.001 \set delta random(-5000, 5000)
|
|
0.326 BEGIN;
|
|
0.603 UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;
|
|
0.454 SELECT abalance FROM pgbench_accounts WHERE aid = :aid;
|
|
5.528 UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;
|
|
7.335 UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;
|
|
0.371 INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);
|
|
1.212 END;
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
If multiple script files are specified, the averages are reported
|
|
separately for each script file.
|
|
</para>
|
|
|
|
<para>
|
|
Note that collecting the additional timing information needed for
|
|
per-statement latency computation adds some overhead. This will slow
|
|
average execution speed and lower the computed TPS. The amount
|
|
of slowdown varies significantly depending on platform and hardware.
|
|
Comparing average TPS values with and without latency reporting enabled
|
|
is a good way to measure if the timing overhead is significant.
|
|
</para>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Good Practices</title>
|
|
|
|
<para>
|
|
It is very easy to use <application>pgbench</application> to produce completely
|
|
meaningless numbers. Here are some guidelines to help you get useful
|
|
results.
|
|
</para>
|
|
|
|
<para>
|
|
In the first place, <emphasis>never</emphasis> believe any test that runs
|
|
for only a few seconds. Use the <option>-t</option> or <option>-T</option> option
|
|
to make the run last at least a few minutes, so as to average out noise.
|
|
In some cases you could need hours to get numbers that are reproducible.
|
|
It's a good idea to try the test run a few times, to find out if your
|
|
numbers are reproducible or not.
|
|
</para>
|
|
|
|
<para>
|
|
For the default TPC-B-like test scenario, the initialization scale factor
|
|
(<option>-s</option>) should be at least as large as the largest number of
|
|
clients you intend to test (<option>-c</option>); else you'll mostly be
|
|
measuring update contention. There are only <option>-s</option> rows in
|
|
the <structname>pgbench_branches</structname> table, and every transaction wants to
|
|
update one of them, so <option>-c</option> values in excess of <option>-s</option>
|
|
will undoubtedly result in lots of transactions blocked waiting for
|
|
other transactions.
|
|
</para>
|
|
|
|
<para>
|
|
The default test scenario is also quite sensitive to how long it's been
|
|
since the tables were initialized: accumulation of dead rows and dead space
|
|
in the tables changes the results. To understand the results you must keep
|
|
track of the total number of updates and when vacuuming happens. If
|
|
autovacuum is enabled it can result in unpredictable changes in measured
|
|
performance.
|
|
</para>
|
|
|
|
<para>
|
|
A limitation of <application>pgbench</application> is that it can itself become
|
|
the bottleneck when trying to test a large number of client sessions.
|
|
This can be alleviated by running <application>pgbench</application> on a different
|
|
machine from the database server, although low network latency will be
|
|
essential. It might even be useful to run several <application>pgbench</application>
|
|
instances concurrently, on several client machines, against the same
|
|
database server.
|
|
</para>
|
|
</refsect2>
|
|
<refsect2>
|
|
<title>Security</title>
|
|
|
|
<para>
|
|
If untrusted users have access to a database that has not adopted a
|
|
<link linkend="ddl-schemas-patterns">secure schema usage pattern</link>,
|
|
do not run <application>pgbench</application> in that
|
|
database. <application>pgbench</application> uses unqualified names and
|
|
does not manipulate the search path.
|
|
</para>
|
|
</refsect2>
|
|
</refsect1>
|
|
</refentry>
|