<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>pgbench</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="app-pgbasebackup.html" title="pg_basebackup" /><link rel="next" href="app-pgconfig.html" title="pg_config" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center"><span xmlns="http://www.w3.org/1999/xhtml" class="application">pgbench</span></th></tr><tr><td width="10%" align="left"><a accesskey="p" href="app-pgbasebackup.html" title="pg_basebackup">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="reference-client.html" title="PostgreSQL Client Applications">Up</a></td><th width="60%" align="center">PostgreSQL Client Applications</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="app-pgconfig.html" title="pg_config">Next</a></td></tr></table><hr></hr></div><div class="refentry" id="PGBENCH"><div class="titlepage"></div><a id="id-1.9.4.10.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle"><span class="application">pgbench</span></span></h2><p>pgbench — run a benchmark test on <span class="productname">PostgreSQL</span></p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="cmdsynopsis"><p id="id-1.9.4.10.4.1"><code class="command">pgbench</code> <code class="option">-i</code> [<em class="replaceable"><code>option</code></em>...] [<em class="replaceable"><code>dbname</code></em>]</p></div><div class="cmdsynopsis"><p id="id-1.9.4.10.4.2"><code class="command">pgbench</code> [<em class="replaceable"><code>option</code></em>...] [<em class="replaceable"><code>dbname</code></em>]</p></div></div><div class="refsect1" id="id-1.9.4.10.5"><h2>Description</h2><p>
<span class="application">pgbench</span> is a simple program for running benchmark
tests on <span class="productname">PostgreSQL</span>. It runs the same sequence of SQL
commands over and over, possibly in multiple concurrent database sessions,
and then calculates the average transaction rate (transactions per second).
By default, <span class="application">pgbench</span> tests a scenario that is
loosely based on TPC-B, involving five <code class="command">SELECT</code>,
<code class="command">UPDATE</code>, and <code class="command">INSERT</code> commands per transaction.
However, it is easy to test other cases by writing your own transaction
script files.
</p><p>
Typical output from <span class="application">pgbench</span> looks like:
</p><pre class="screen">
transaction type: <builtin: TPC-B (sort of)>
scaling factor: 10
query mode: simple
number of clients: 10
number of threads: 1
number of transactions per client: 1000
number of transactions actually processed: 10000/10000
tps = 85.184871 (including connections establishing)
tps = 85.296346 (excluding connections establishing)
</pre><p>
The first six lines report some of the most important parameter
settings. The next line reports the number of transactions completed
and intended (the latter being just the product of number of clients
and number of transactions per client); these will be equal unless the run
failed before completion. (In <code class="option">-T</code> mode, only the actual
number of transactions is printed.)
The last two lines report the number of transactions per second,
figured with and without counting the time to start database sessions.
</p><p>
The default TPC-B-like transaction test requires specific tables to be
set up beforehand. <span class="application">pgbench</span> should be invoked with
the <code class="option">-i</code> (initialize) option to create and populate these
tables. (When you are testing a custom script, you don't need this
step, but will instead need to do whatever setup your test needs.)
Initialization looks like:
</p><pre class="programlisting">
pgbench -i [<span class="optional"> <em class="replaceable"><code>other-options</code></em> </span>] <em class="replaceable"><code>dbname</code></em>
</pre><p>
where <em class="replaceable"><code>dbname</code></em> is the name of the already-created
database to test in. (You may also need <code class="option">-h</code>,
<code class="option">-p</code>, and/or <code class="option">-U</code> options to specify how to
connect to the database server.)
</p><div class="caution"><h3 class="title">Caution</h3><p>
<code class="literal">pgbench -i</code> creates four tables <code class="structname">pgbench_accounts</code>,
<code class="structname">pgbench_branches</code>, <code class="structname">pgbench_history</code>, and
<code class="structname">pgbench_tellers</code>,
destroying any existing tables of these names.
Be very careful to use another database if you have tables having these
names!
</p></div><p>
At the default <span class="quote">“<span class="quote">scale factor</span>”</span> of 1, the tables initially
contain this many rows:
</p><pre class="screen">
table # of rows
---------------------------------
pgbench_branches 1
pgbench_tellers 10
pgbench_accounts 100000
pgbench_history 0
</pre><p>
You can (and, for most purposes, probably should) increase the number
of rows by using the <code class="option">-s</code> (scale factor) option. The
<code class="option">-F</code> (fillfactor) option might also be used at this point.
</p><p>
Once you have done the necessary setup, you can run your benchmark
with a command that doesn't include <code class="option">-i</code>, that is
</p><pre class="programlisting">
pgbench [<span class="optional"> <em class="replaceable"><code>options</code></em> </span>] <em class="replaceable"><code>dbname</code></em>
</pre><p>
In nearly all cases, you'll need some options to make a useful test.
The most important options are <code class="option">-c</code> (number of clients),
<code class="option">-t</code> (number of transactions), <code class="option">-T</code> (time limit),
and <code class="option">-f</code> (specify a custom script file).
See below for a full list.
</p></div><div class="refsect1" id="id-1.9.4.10.6"><h2>Options</h2><p>
The following is divided into three subsections. Different options are
used during database initialization and while running benchmarks, but some
options are useful in both cases.
</p><div class="refsect2" id="PGBENCH-INIT-OPTIONS"><h3>Initialization Options</h3><p>
<span class="application">pgbench</span> accepts the following command-line
initialization arguments:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="option">-i</code><br /></span><span class="term"><code class="option">--initialize</code></span></dt><dd><p>
Required to invoke initialization mode.
</p></dd><dt><span class="term"><code class="option">-I <em class="replaceable"><code>init_steps</code></em></code><br /></span><span class="term"><code class="option">--init-steps=<em class="replaceable"><code>init_steps</code></em></code></span></dt><dd><p>
Perform just a selected set of the normal initialization steps.
<em class="replaceable"><code>init_steps</code></em> specifies the
initialization steps to be performed, using one character per step.
Each step is invoked in the specified order.
The default is <code class="literal">dtgvp</code>.
The available steps are:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">d</code> (Drop)</span></dt><dd><p>
Drop any existing <span class="application">pgbench</span> tables.
</p></dd><dt><span class="term"><code class="literal">t</code> (create Tables)</span></dt><dd><p>
Create the tables used by the
standard <span class="application">pgbench</span> scenario, namely
<code class="structname">pgbench_accounts</code>,
<code class="structname">pgbench_branches</code>,
<code class="structname">pgbench_history</code>, and
<code class="structname">pgbench_tellers</code>.
</p></dd><dt><span class="term"><code class="literal">g</code> (Generate data)</span></dt><dd><p>
Generate data and load it into the standard tables,
replacing any data already present.
</p></dd><dt><span class="term"><code class="literal">v</code> (Vacuum)</span></dt><dd><p>
Invoke <code class="command">VACUUM</code> on the standard tables.
</p></dd><dt><span class="term"><code class="literal">p</code> (create Primary keys)</span></dt><dd><p>
Create primary key indexes on the standard tables.
</p></dd><dt><span class="term"><code class="literal">f</code> (create Foreign keys)</span></dt><dd><p>
Create foreign key constraints between the standard tables.
(Note that this step is not performed by default.)
</p></dd></dl></div><p>
</p></dd><dt><span class="term"><code class="option">-F</code> <em class="replaceable"><code>fillfactor</code></em><br /></span><span class="term"><code class="option">--fillfactor=</code><em class="replaceable"><code>fillfactor</code></em></span></dt><dd><p>
Create the <code class="structname">pgbench_accounts</code>,
<code class="structname">pgbench_tellers</code> and
<code class="structname">pgbench_branches</code> tables with the given fillfactor.
Default is 100.
</p></dd><dt><span class="term"><code class="option">-n</code><br /></span><span class="term"><code class="option">--no-vacuum</code></span></dt><dd><p>
Perform no vacuuming during initialization.
(This option suppresses the <code class="literal">v</code> initialization step,
even if it was specified in <code class="option">-I</code>.)
</p></dd><dt><span class="term"><code class="option">-q</code><br /></span><span class="term"><code class="option">--quiet</code></span></dt><dd><p>
Switch logging to quiet mode, producing only one progress message per 5
seconds. The default logging prints one message each 100000 rows, which
often outputs many lines per second (especially on good hardware).
</p></dd><dt><span class="term"><code class="option">-s</code> <em class="replaceable"><code>scale_factor</code></em><br /></span><span class="term"><code class="option">--scale=</code><em class="replaceable"><code>scale_factor</code></em></span></dt><dd><p>
Multiply the number of rows generated by the scale factor.
For example, <code class="literal">-s 100</code> will create 10,000,000 rows
in the <code class="structname">pgbench_accounts</code> table. Default is 1.
When the scale is 20,000 or larger, the columns used to
hold account identifiers (<code class="structfield">aid</code> columns)
will switch to using larger integers (<code class="type">bigint</code>),
in order to be big enough to hold the range of account
identifiers.
</p></dd><dt><span class="term"><code class="option">--foreign-keys</code></span></dt><dd><p>
Create foreign key constraints between the standard tables.
(This option adds the <code class="literal">f</code> step to the initialization
step sequence, if it is not already present.)
</p></dd><dt><span class="term"><code class="option">--index-tablespace=<em class="replaceable"><code>index_tablespace</code></em></code></span></dt><dd><p>
Create indexes in the specified tablespace, rather than the default
tablespace.
</p></dd><dt><span class="term"><code class="option">--tablespace=<em class="replaceable"><code>tablespace</code></em></code></span></dt><dd><p>
Create tables in the specified tablespace, rather than the default
tablespace.
</p></dd><dt><span class="term"><code class="option">--unlogged-tables</code></span></dt><dd><p>
Create all tables as unlogged tables, rather than permanent tables.
</p></dd></dl></div><p>
</p></div><div class="refsect2" id="PGBENCH-RUN-OPTIONS"><h3>Benchmarking Options</h3><p>
<span class="application">pgbench</span> accepts the following command-line
benchmarking arguments:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="option">-b</code> <em class="replaceable"><code>scriptname[@weight]</code></em><br /></span><span class="term"><code class="option">--builtin</code>=<em class="replaceable"><code>scriptname[@weight]</code></em></span></dt><dd><p>
Add the specified built-in script to the list of executed scripts.
An optional integer weight after <code class="literal">@</code> allows to adjust the
probability of drawing the script. If not specified, it is set to 1.
Available built-in scripts are: <code class="literal">tpcb-like</code>,
<code class="literal">simple-update</code> and <code class="literal">select-only</code>.
Unambiguous prefixes of built-in names are accepted.
With special name <code class="literal">list</code>, show the list of built-in scripts
and exit immediately.
</p></dd><dt><span class="term"><code class="option">-c</code> <em class="replaceable"><code>clients</code></em><br /></span><span class="term"><code class="option">--client=</code><em class="replaceable"><code>clients</code></em></span></dt><dd><p>
Number of clients simulated, that is, number of concurrent database
sessions. Default is 1.
</p></dd><dt><span class="term"><code class="option">-C</code><br /></span><span class="term"><code class="option">--connect</code></span></dt><dd><p>
Establish a new connection for each transaction, rather than
doing it just once per client session.
This is useful to measure the connection overhead.
</p></dd><dt><span class="term"><code class="option">-d</code><br /></span><span class="term"><code class="option">--debug</code></span></dt><dd><p>
Print debugging output.
</p></dd><dt><span class="term"><code class="option">-D</code> <em class="replaceable"><code>varname</code></em><code class="literal">=</code><em class="replaceable"><code>value</code></em><br /></span><span class="term"><code class="option">--define=</code><em class="replaceable"><code>varname</code></em><code class="literal">=</code><em class="replaceable"><code>value</code></em></span></dt><dd><p>
Define a variable for use by a custom script (see below).
Multiple <code class="option">-D</code> options are allowed.
</p></dd><dt><span class="term"><code class="option">-f</code> <em class="replaceable"><code>filename[@weight]</code></em><br /></span><span class="term"><code class="option">--file=</code><em class="replaceable"><code>filename[@weight]</code></em></span></dt><dd><p>
Add a transaction script read from <em class="replaceable"><code>filename</code></em> to
the list of executed scripts.
An optional integer weight after <code class="literal">@</code> allows to adjust the
probability of drawing the test.
See below for details.
</p></dd><dt><span class="term"><code class="option">-j</code> <em class="replaceable"><code>threads</code></em><br /></span><span class="term"><code class="option">--jobs=</code><em class="replaceable"><code>threads</code></em></span></dt><dd><p>
Number of worker threads within <span class="application">pgbench</span>.
Using more than one thread can be helpful on multi-CPU machines.
Clients are distributed as evenly as possible among available threads.
Default is 1.
</p></dd><dt><span class="term"><code class="option">-l</code><br /></span><span class="term"><code class="option">--log</code></span></dt><dd><p>
Write information about each transaction to a log file.
See below for details.
</p></dd><dt><span class="term"><code class="option">-L</code> <em class="replaceable"><code>limit</code></em><br /></span><span class="term"><code class="option">--latency-limit=</code><em class="replaceable"><code>limit</code></em></span></dt><dd><p>
Transactions that last more than <em class="replaceable"><code>limit</code></em> milliseconds
are counted and reported separately, as <em class="firstterm">late</em>.
</p><p>
When throttling is used (<code class="option">--rate=...</code>), transactions that
lag behind schedule by more than <em class="replaceable"><code>limit</code></em> ms, and thus
have no hope of meeting the latency limit, are not sent to the server
at all. They are counted and reported separately as
<em class="firstterm">skipped</em>.
</p></dd><dt><span class="term"><code class="option">-M</code> <em class="replaceable"><code>querymode</code></em><br /></span><span class="term"><code class="option">--protocol=</code><em class="replaceable"><code>querymode</code></em></span></dt><dd><p>
Protocol to use for submitting queries to the server:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><code class="literal">simple</code>: use simple query protocol.</p></li><li class="listitem"><p><code class="literal">extended</code>: use extended query protocol.</p></li><li class="listitem"><p><code class="literal">prepared</code>: use extended query protocol with prepared statements.</p></li></ul></div><p>
The default is simple query protocol. (See <a class="xref" href="protocol.html" title="Chapter 53. Frontend/Backend Protocol">Chapter 53</a>
for more information.)
</p></dd><dt><span class="term"><code class="option">-n</code><br /></span><span class="term"><code class="option">--no-vacuum</code></span></dt><dd><p>
Perform no vacuuming before running the test.
This option is <span class="emphasis"><em>necessary</em></span>
if you are running a custom test scenario that does not include
the standard tables <code class="structname">pgbench_accounts</code>,
<code class="structname">pgbench_branches</code>, <code class="structname">pgbench_history</code>, and
<code class="structname">pgbench_tellers</code>.
</p></dd><dt><span class="term"><code class="option">-N</code><br /></span><span class="term"><code class="option">--skip-some-updates</code></span></dt><dd><p>
Run built-in simple-update script.
Shorthand for <code class="option">-b simple-update</code>.
</p></dd><dt><span class="term"><code class="option">-P</code> <em class="replaceable"><code>sec</code></em><br /></span><span class="term"><code class="option">--progress=</code><em class="replaceable"><code>sec</code></em></span></dt><dd><p>
Show progress report every <em class="replaceable"><code>sec</code></em> 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 (<code class="option">-R</code>),
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.
</p></dd><dt><span class="term"><code class="option">-r</code><br /></span><span class="term"><code class="option">--report-latencies</code></span></dt><dd><p>
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.
</p></dd><dt><span class="term"><code class="option">-R</code> <em class="replaceable"><code>rate</code></em><br /></span><span class="term"><code class="option">--rate=</code><em class="replaceable"><code>rate</code></em></span></dt><dd><p>
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.
</p><p>
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.
</p><p>
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.
</p><p>
If <code class="option">--latency-limit</code> is used together with <code class="option">--rate</code>,
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.
</p><p>
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.
</p></dd><dt><span class="term"><code class="option">-s</code> <em class="replaceable"><code>scale_factor</code></em><br /></span><span class="term"><code class="option">--scale=</code><em class="replaceable"><code>scale_factor</code></em></span></dt><dd><p>
Report the specified scale factor in <span class="application">pgbench</span>'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 <code class="structname">pgbench_branches</code> table.
However, when testing only custom benchmarks (<code class="option">-f</code> option),
the scale factor will be reported as 1 unless this option is used.
</p></dd><dt><span class="term"><code class="option">-S</code><br /></span><span class="term"><code class="option">--select-only</code></span></dt><dd><p>
Run built-in select-only script.
Shorthand for <code class="option">-b select-only</code>.
</p></dd><dt><span class="term"><code class="option">-t</code> <em class="replaceable"><code>transactions</code></em><br /></span><span class="term"><code class="option">--transactions=</code><em class="replaceable"><code>transactions</code></em></span></dt><dd><p>
Number of transactions each client runs. Default is 10.
</p></dd><dt><span class="term"><code class="option">-T</code> <em class="replaceable"><code>seconds</code></em><br /></span><span class="term"><code class="option">--time=</code><em class="replaceable"><code>seconds</code></em></span></dt><dd><p>
Run the test for this many seconds, rather than a fixed number of
transactions per client. <code class="option">-t</code> and
<code class="option">-T</code> are mutually exclusive.
</p></dd><dt><span class="term"><code class="option">-v</code><br /></span><span class="term"><code class="option">--vacuum-all</code></span></dt><dd><p>
Vacuum all four standard tables before running the test.
With neither <code class="option">-n</code> nor <code class="option">-v</code>, <span class="application">pgbench</span> will vacuum the
<code class="structname">pgbench_tellers</code> and <code class="structname">pgbench_branches</code>
tables, and will truncate <code class="structname">pgbench_history</code>.
</p></dd><dt><span class="term"><code class="option">--aggregate-interval=<em class="replaceable"><code>seconds</code></em></code></span></dt><dd><p>
Length of aggregation interval (in seconds). May be used only
with <code class="option">-l</code> option. With this option, the log contains
per-interval summary data, as described below.
</p></dd><dt><span class="term"><code class="option">--log-prefix=<em class="replaceable"><code>prefix</code></em></code></span></dt><dd><p>
Set the filename prefix for the log files created by
<code class="option">--log</code>. The default is <code class="literal">pgbench_log</code>.
</p></dd><dt><span class="term"><code class="option">--progress-timestamp</code></span></dt><dd><p>
When showing progress (option <code class="option">-P</code>), 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.
</p></dd><dt><span class="term"><code class="option">--random-seed=</code><em class="replaceable"><code>SEED</code></em></span></dt><dd><p>
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 <em class="replaceable"><code>SEED</code></em> may be:
<code class="literal">time</code> (the default, the seed is based on the current time),
<code class="literal">rand</code> (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
(<code class="literal">random...</code> functions) or implicitly (for instance option
<code class="option">--rate</code> uses it to schedule transactions).
When explicitly set, the value used for seeding is shown on the terminal.
Any value allowed for <em class="replaceable"><code>SEED</code></em> may also be
provided through the environment variable
<code class="literal">PGBENCH_RANDOM_SEED</code>.
To ensure that the provided seed impacts all possible uses, put this option
first or use the environment variable.
</p><p>
Setting the seed explicitly allows to reproduce a <code class="command">pgbench</code>
run exactly, as far as random numbers are concerned.
As the random state is managed per thread, this means the exact same
<code class="command">pgbench</code> 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.
</p></dd><dt><span class="term"><code class="option">--sampling-rate=<em class="replaceable"><code>rate</code></em></code></span></dt><dd><p>
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.
</p><p>
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).
</p></dd></dl></div><p>
</p></div><div class="refsect2" id="PGBENCH-COMMON-OPTIONS"><h3>Common Options</h3><p>
<span class="application">pgbench</span> accepts the following command-line
common arguments:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="option">-h</code> <em class="replaceable"><code>hostname</code></em><br /></span><span class="term"><code class="option">--host=</code><em class="replaceable"><code>hostname</code></em></span></dt><dd><p>
The database server's host name
</p></dd><dt><span class="term"><code class="option">-p</code> <em class="replaceable"><code>port</code></em><br /></span><span class="term"><code class="option">--port=</code><em class="replaceable"><code>port</code></em></span></dt><dd><p>
The database server's port number
</p></dd><dt><span class="term"><code class="option">-U</code> <em class="replaceable"><code>login</code></em><br /></span><span class="term"><code class="option">--username=</code><em class="replaceable"><code>login</code></em></span></dt><dd><p>
The user name to connect as
</p></dd><dt><span class="term"><code class="option">-V</code><br /></span><span class="term"><code class="option">--version</code></span></dt><dd><p>
Print the <span class="application">pgbench</span> version and exit.
</p></dd><dt><span class="term"><code class="option">-?</code><br /></span><span class="term"><code class="option">--help</code></span></dt><dd><p>
Show help about <span class="application">pgbench</span> command line
arguments, and exit.
</p></dd></dl></div><p>
</p></div></div><div class="refsect1" id="id-1.9.4.10.7"><h2>Notes</h2><div class="refsect2" id="id-1.9.4.10.7.2"><h3>What is the <span class="quote">“<span class="quote">Transaction</span>”</span> Actually Performed in <span class="application">pgbench</span>?</h3><p>
<span class="application">pgbench</span> executes test scripts chosen randomly
from a specified list.
They include built-in scripts with <code class="option">-b</code> and
user-provided custom scripts with <code class="option">-f</code>.
Each script may be given a relative weight specified after a
<code class="literal">@</code> so as to change its drawing probability.
The default weight is <code class="literal">1</code>.
Scripts with a weight of <code class="literal">0</code> are ignored.
</p><p>
The default built-in transaction script (also invoked with <code class="option">-b tpcb-like</code>)
issues seven commands per transaction over randomly chosen <code class="literal">aid</code>,
<code class="literal">tid</code>, <code class="literal">bid</code> and <code class="literal">delta</code>.
The scenario is inspired by the TPC-B benchmark, but is not actually TPC-B,
hence the name.
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p><code class="literal">BEGIN;</code></p></li><li class="listitem"><p><code class="literal">UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;</code></p></li><li class="listitem"><p><code class="literal">SELECT abalance FROM pgbench_accounts WHERE aid = :aid;</code></p></li><li class="listitem"><p><code class="literal">UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;</code></p></li><li class="listitem"><p><code class="literal">UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;</code></p></li><li class="listitem"><p><code class="literal">INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);</code></p></li><li class="listitem"><p><code class="literal">END;</code></p></li></ol></div><p>
If you select the <code class="literal">simple-update</code> built-in (also <code class="option">-N</code>),
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.
</p><p>
If you select the <code class="literal">select-only</code> built-in (also <code class="option">-S</code>),
only the <code class="command">SELECT</code> is issued.
</p></div><div class="refsect2" id="id-1.9.4.10.7.3"><h3>Custom Scripts</h3><p>
<span class="application">pgbench</span> has support for running custom
benchmark scenarios by replacing the default transaction script
(described above) with a transaction script read from a file
(<code class="option">-f</code> option). In this case a <span class="quote">“<span class="quote">transaction</span>”</span>
counts as one execution of a script file.
</p><p>
A script file contains one or more SQL commands terminated by
semicolons. Empty lines and lines beginning with
<code class="literal">--</code> are ignored. Script files can also contain
<span class="quote">“<span class="quote">meta commands</span>”</span>, which are interpreted by <span class="application">pgbench</span>
itself, as described below.
</p><div class="note"><h3 class="title">Note</h3><p>
Before <span class="productname">PostgreSQL</span> 9.6, SQL commands in script files
were terminated by newlines, and so they could not be continued across
lines. Now a semicolon is <span class="emphasis"><em>required</em></span> 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 <span class="application">pgbench</span>, be sure to write
each SQL command on a single line ending with a semicolon.
</p></div><p>
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 <code class="option">-D</code> option,
explained above, or by the meta commands explained below.
In addition to any variables preset by <code class="option">-D</code> command-line options,
there are a few variables that are preset automatically, listed in
<a class="xref" href="pgbench.html#PGBENCH-AUTOMATIC-VARIABLES" title="Table 241. Automatic Variables">Table 241</a>. A value specified for these
variables using <code class="option">-D</code> takes precedence over the automatic presets.
Once set, a variable's
value can be inserted into a SQL command by writing
<code class="literal">:</code><em class="replaceable"><code>variablename</code></em>. When running more than
one client session, each session has its own set of variables.
</p><div class="table" id="PGBENCH-AUTOMATIC-VARIABLES"><p class="title"><strong>Table 241. Automatic Variables</strong></p><div class="table-contents"><table class="table" summary="Automatic Variables" border="1"><colgroup><col /><col /></colgroup><thead><tr><th>Variable</th><th>Description</th></tr></thead><tbody><tr><td> <code class="literal">client_id</code> </td><td>unique number identifying the client session (starts from zero)</td></tr><tr><td> <code class="literal">default_seed</code> </td><td>seed used in hash functions by default</td></tr><tr><td> <code class="literal">random_seed</code> </td><td>random generator seed (unless overwritten with <code class="option">-D</code>)</td></tr><tr><td> <code class="literal">scale</code> </td><td>current scale factor</td></tr></tbody></table></div></div><br class="table-break" /><p>
Script file meta commands begin with a backslash (<code class="literal">\</code>) 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:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">\if</code> <em class="replaceable"><code>expression</code></em><br /></span><span class="term"><code class="literal">\elif</code> <em class="replaceable"><code>expression</code></em><br /></span><span class="term"><code class="literal">\else</code><br /></span><span class="term"><code class="literal">\endif</code></span></dt><dd><p>
This group of commands implements nestable conditional blocks,
similarly to <code class="literal">psql</code>'s <a class="xref" href="app-psql.html#PSQL-METACOMMAND-IF"><code class="literal">\if</code> <em class="replaceable"><code>expression</code></em></a>.
Conditional expressions are identical to those with <code class="literal">\set</code>,
with non-zero values interpreted as true.
</p></dd><dt id="PGBENCH-METACOMMAND-SET"><span class="term">
<code class="literal">\set <em class="replaceable"><code>varname</code></em> <em class="replaceable"><code>expression</code></em></code>
</span></dt><dd><p>
Sets variable <em class="replaceable"><code>varname</code></em> to a value calculated
from <em class="replaceable"><code>expression</code></em>.
The expression may contain the <code class="literal">NULL</code> constant,
Boolean constants <code class="literal">TRUE</code> and <code class="literal">FALSE</code>,
integer constants such as <code class="literal">5432</code>,
double constants such as <code class="literal">3.14159</code>,
references to variables <code class="literal">:</code><em class="replaceable"><code>variablename</code></em>,
<a class="link" href="pgbench.html#PGBENCH-BUILTIN-OPERATORS" title="Built-In Operators">operators</a>
with their usual SQL precedence and associativity,
<a class="link" href="pgbench.html#PGBENCH-BUILTIN-FUNCTIONS" title="Built-In Functions">function calls</a>,
SQL <a class="link" href="functions-conditional.html#FUNCTIONS-CASE" title="9.17.1. CASE"><code class="token">CASE</code> generic conditional
expressions</a> and parentheses.
</p><p>
Functions and most operators return <code class="literal">NULL</code> on
<code class="literal">NULL</code> input.
</p><p>
For conditional purposes, non zero numerical values are
<code class="literal">TRUE</code>, zero numerical values and <code class="literal">NULL</code>
are <code class="literal">FALSE</code>.
</p><p>
When no final <code class="token">ELSE</code> clause is provided to a
<code class="token">CASE</code>, the default value is <code class="literal">NULL</code>.
</p><p>
Examples:
</p><pre class="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
</pre></dd><dt><span class="term">
<code class="literal">\sleep <em class="replaceable"><code>number</code></em> [ us | ms | s ]</code>
</span></dt><dd><p>
Causes script execution to sleep for the specified duration in
microseconds (<code class="literal">us</code>), milliseconds (<code class="literal">ms</code>) or seconds
(<code class="literal">s</code>). If the unit is omitted then seconds are the default.
<em class="replaceable"><code>number</code></em> can be either an integer constant or a
<code class="literal">:</code><em class="replaceable"><code>variablename</code></em> reference to a variable
having an integer value.
</p><p>
Example:
</p><pre class="programlisting">
\sleep 10 ms
</pre></dd><dt><span class="term">
<code class="literal">\setshell <em class="replaceable"><code>varname</code></em> <em class="replaceable"><code>command</code></em> [ <em class="replaceable"><code>argument</code></em> ... ]</code>
</span></dt><dd><p>
Sets variable <em class="replaceable"><code>varname</code></em> to the result of the shell command
<em class="replaceable"><code>command</code></em> with the given <em class="replaceable"><code>argument</code></em>(s).
The command must return an integer value through its standard output.
</p><p>
<em class="replaceable"><code>command</code></em> and each <em class="replaceable"><code>argument</code></em> can be either
a text constant or a <code class="literal">:</code><em class="replaceable"><code>variablename</code></em> reference
to a variable. If you want to use an <em class="replaceable"><code>argument</code></em> starting
with a colon, write an additional colon at the beginning of
<em class="replaceable"><code>argument</code></em>.
</p><p>
Example:
</p><pre class="programlisting">
\setshell variable_to_be_assigned command literal_argument :variable ::literal_starting_with_colon
</pre></dd><dt><span class="term">
<code class="literal">\shell <em class="replaceable"><code>command</code></em> [ <em class="replaceable"><code>argument</code></em> ... ]</code>
</span></dt><dd><p>
Same as <code class="literal">\setshell</code>, but the result of the command
is discarded.
</p><p>
Example:
</p><pre class="programlisting">
\shell command literal_argument :variable ::literal_starting_with_colon
</pre></dd></dl></div></div><div class="refsect2" id="PGBENCH-BUILTIN-OPERATORS"><h3>Built-In Operators</h3><p>
The arithmetic, bitwise, comparison and logical operators listed in
<a class="xref" href="pgbench.html#PGBENCH-OPERATORS" title="Table 242. pgbench Operators by increasing precedence">Table 242</a> are built into <span class="application">pgbench</span>
and may be used in expressions appearing in
<a class="link" href="pgbench.html#PGBENCH-METACOMMAND-SET"><code class="literal">\set</code></a>.
</p><div class="table" id="PGBENCH-OPERATORS"><p class="title"><strong>Table 242. pgbench Operators by increasing precedence</strong></p><div class="table-contents"><table class="table" summary="pgbench Operators by increasing precedence" border="1"><colgroup><col /><col /><col /><col /></colgroup><thead><tr><th>Operator</th><th>Description</th><th>Example</th><th>Result</th></tr></thead><tbody><tr><td><code class="literal">OR</code></td><td>logical or</td><td><code class="literal">5 or 0</code></td><td><code class="literal">TRUE</code></td></tr><tr><td><code class="literal">AND</code></td><td>logical and</td><td><code class="literal">3 and 0</code></td><td><code class="literal">FALSE</code></td></tr><tr><td><code class="literal">NOT</code></td><td>logical not</td><td><code class="literal">not false</code></td><td><code class="literal">TRUE</code></td></tr><tr><td><code class="literal">IS [NOT] (NULL|TRUE|FALSE)</code></td><td>value tests</td><td><code class="literal">1 is null</code></td><td><code class="literal">FALSE</code></td></tr><tr><td><code class="literal">ISNULL|NOTNULL</code></td><td>null tests</td><td><code class="literal">1 notnull</code></td><td><code class="literal">TRUE</code></td></tr><tr><td><code class="literal">=</code></td><td>is equal</td><td><code class="literal">5 = 4</code></td><td><code class="literal">FALSE</code></td></tr><tr><td><code class="literal"><></code></td><td>is not equal</td><td><code class="literal">5 <> 4</code></td><td><code class="literal">TRUE</code></td></tr><tr><td><code class="literal">!=</code></td><td>is not equal</td><td><code class="literal">5 != 5</code></td><td><code class="literal">FALSE</code></td></tr><tr><td><code class="literal"><</code></td><td>lower than</td><td><code class="literal">5 < 4</code></td><td><code class="literal">FALSE</code></td></tr><tr><td><code class="literal"><=</code></td><td>lower or equal</td><td><code class="literal">5 <= 4</code></td><td><code class="literal">FALSE</code></td></tr><tr><td><code class="literal">></code></td><td>greater than</td><td><code class="literal">5 > 4</code></td><td><code class="literal">TRUE</code></td></tr><tr><td><code class="literal">>=</code></td><td>greater or equal</td><td><code class="literal">5 >= 4</code></td><td><code class="literal">TRUE</code></td></tr><tr><td><code class="literal">|</code></td><td>integer bitwise OR</td><td><code class="literal">1 | 2</code></td><td><code class="literal">3</code></td></tr><tr><td><code class="literal">#</code></td><td>integer bitwise XOR</td><td><code class="literal">1 # 3</code></td><td><code class="literal">2</code></td></tr><tr><td><code class="literal">&</code></td><td>integer bitwise AND</td><td><code class="literal">1 & 3</code></td><td><code class="literal">1</code></td></tr><tr><td><code class="literal">~</code></td><td>integer bitwise NOT</td><td><code class="literal">~ 1</code></td><td><code class="literal">-2</code></td></tr><tr><td><code class="literal"><<</code></td><td>integer bitwise shift left</td><td><code class="literal">1 << 2</code></td><td><code class="literal">4</code></td></tr><tr><td><code class="literal">>></code></td><td>integer bitwise shift right</td><td><code class="literal">8 >> 2</code></td><td><code class="literal">2</code></td></tr><tr><td><code class="literal">+</code></td><td>addition</td><td><code class="literal">5 + 4</code></td><td><code class="literal">9</code></td></tr><tr><td><code class="literal">-</code></td><td>subtraction</td><td><code class="literal">3 - 2.0</code></td><td><code class="literal">1.0</code></td></tr><tr><td><code class="literal">*</code></td><td>multiplication</td><td><code class="literal">5 * 4</code></td><td><code class="literal">20</code></td></tr><tr><td><code class="literal">/</code></td><td>division (integer truncates the results)</td><td><code class="literal">5 / 3</code></td><td><code class="literal">1</code></td></tr><tr><td><code class="literal">%</code></td><td>modulo</td><td><code class="literal">3 % 2</code></td><td><code class="literal">1</code></td></tr><tr><td><code class="literal">-</code></td><td>opposite</td><td><code class="literal">- 2.0</code></td><td><code class="literal">-2.0</code></td></tr></tbody></table></div></div><br class="table-break" /></div><div class="refsect2" id="PGBENCH-BUILTIN-FUNCTIONS"><h3>Built-In Functions</h3><p>
The functions listed in <a class="xref" href="pgbench.html#PGBENCH-FUNCTIONS" title="Table 243. pgbench Functions">Table 243</a> are built
into <span class="application">pgbench</span> and may be used in expressions appearing in
<a class="link" href="pgbench.html#PGBENCH-METACOMMAND-SET"><code class="literal">\set</code></a>.
</p><div class="table" id="PGBENCH-FUNCTIONS"><p class="title"><strong>Table 243. pgbench Functions</strong></p><div class="table-contents"><table class="table" summary="pgbench Functions" border="1"><colgroup><col /><col /><col /><col /><col /></colgroup><thead><tr><th>Function</th><th>Return Type</th><th>Description</th><th>Example</th><th>Result</th></tr></thead><tbody><tr><td><code class="literal"><code class="function">abs(<em class="replaceable"><code>a</code></em>)</code></code></td><td>same as <em class="replaceable"><code>a</code></em></td><td>absolute value</td><td><code class="literal">abs(-17)</code></td><td><code class="literal">17</code></td></tr><tr><td><code class="literal"><code class="function">debug(<em class="replaceable"><code>a</code></em>)</code></code></td><td>same as <em class="replaceable"><code>a</code></em> </td><td>print <em class="replaceable"><code>a</code></em> to <span class="systemitem">stderr</span>,
and return <em class="replaceable"><code>a</code></em></td><td><code class="literal">debug(5432.1)</code></td><td><code class="literal">5432.1</code></td></tr><tr><td><code class="literal"><code class="function">double(<em class="replaceable"><code>i</code></em>)</code></code></td><td>double</td><td>cast to double</td><td><code class="literal">double(5432)</code></td><td><code class="literal">5432.0</code></td></tr><tr><td><code class="literal"><code class="function">exp(<em class="replaceable"><code>x</code></em>)</code></code></td><td>double</td><td>exponential</td><td><code class="literal">exp(1.0)</code></td><td><code class="literal">2.718281828459045</code></td></tr><tr><td><code class="literal"><code class="function">greatest(<em class="replaceable"><code>a</code></em> [, <em class="replaceable"><code>...</code></em> ] )</code></code></td><td>double if any <em class="replaceable"><code>a</code></em> is double, else integer</td><td>largest value among arguments</td><td><code class="literal">greatest(5, 4, 3, 2)</code></td><td><code class="literal">5</code></td></tr><tr><td><code class="literal"><code class="function">hash(<em class="replaceable"><code>a</code></em> [, <em class="replaceable"><code>seed</code></em> ] )</code></code></td><td>integer</td><td>alias for <code class="literal">hash_murmur2()</code></td><td><code class="literal">hash(10, 5432)</code></td><td><code class="literal">-5817877081768721676</code></td></tr><tr><td><code class="literal"><code class="function">hash_fnv1a(<em class="replaceable"><code>a</code></em> [, <em class="replaceable"><code>seed</code></em> ] )</code></code></td><td>integer</td><td><a class="ulink" href="https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function" target="_top">FNV-1a hash</a></td><td><code class="literal">hash_fnv1a(10, 5432)</code></td><td><code class="literal">-7793829335365542153</code></td></tr><tr><td><code class="literal"><code class="function">hash_murmur2(<em class="replaceable"><code>a</code></em> [, <em class="replaceable"><code>seed</code></em> ] )</code></code></td><td>integer</td><td><a class="ulink" href="https://en.wikipedia.org/wiki/MurmurHash" target="_top">MurmurHash2 hash</a></td><td><code class="literal">hash_murmur2(10, 5432)</code></td><td><code class="literal">-5817877081768721676</code></td></tr><tr><td><code class="literal"><code class="function">int(<em class="replaceable"><code>x</code></em>)</code></code></td><td>integer</td><td>cast to int</td><td><code class="literal">int(5.4 + 3.8)</code></td><td><code class="literal">9</code></td></tr><tr><td><code class="literal"><code class="function">least(<em class="replaceable"><code>a</code></em> [, <em class="replaceable"><code>...</code></em> ] )</code></code></td><td>double if any <em class="replaceable"><code>a</code></em> is double, else integer</td><td>smallest value among arguments</td><td><code class="literal">least(5, 4, 3, 2.1)</code></td><td><code class="literal">2.1</code></td></tr><tr><td><code class="literal"><code class="function">ln(<em class="replaceable"><code>x</code></em>)</code></code></td><td>double</td><td>natural logarithm</td><td><code class="literal">ln(2.718281828459045)</code></td><td><code class="literal">1.0</code></td></tr><tr><td><code class="literal"><code class="function">mod(<em class="replaceable"><code>i</code></em>, <em class="replaceable"><code>j</code></em>)</code></code></td><td>integer</td><td>modulo</td><td><code class="literal">mod(54, 32)</code></td><td><code class="literal">22</code></td></tr><tr><td><code class="literal"><code class="function">pi()</code></code></td><td>double</td><td>value of the constant PI</td><td><code class="literal">pi()</code></td><td><code class="literal">3.14159265358979323846</code></td></tr><tr><td><code class="literal"><code class="function">pow(<em class="replaceable"><code>x</code></em>, <em class="replaceable"><code>y</code></em>)</code>, <code class="function">power(<em class="replaceable"><code>x</code></em>, <em class="replaceable"><code>y</code></em>)</code></code></td><td>double</td><td>exponentiation</td><td><code class="literal">pow(2.0, 10)</code>, <code class="literal">power(2.0, 10)</code></td><td><code class="literal">1024.0</code></td></tr><tr><td><code class="literal"><code class="function">random(<em class="replaceable"><code>lb</code></em>, <em class="replaceable"><code>ub</code></em>)</code></code></td><td>integer</td><td>uniformly-distributed random integer in <code class="literal">[lb, ub]</code></td><td><code class="literal">random(1, 10)</code></td><td>an integer between <code class="literal">1</code> and <code class="literal">10</code></td></tr><tr><td><code class="literal"><code class="function">random_exponential(<em class="replaceable"><code>lb</code></em>, <em class="replaceable"><code>ub</code></em>, <em class="replaceable"><code>parameter</code></em>)</code></code></td><td>integer</td><td>exponentially-distributed random integer in <code class="literal">[lb, ub]</code>,
see below</td><td><code class="literal">random_exponential(1, 10, 3.0)</code></td><td>an integer between <code class="literal">1</code> and <code class="literal">10</code></td></tr><tr><td><code class="literal"><code class="function">random_gaussian(<em class="replaceable"><code>lb</code></em>, <em class="replaceable"><code>ub</code></em>, <em class="replaceable"><code>parameter</code></em>)</code></code></td><td>integer</td><td>Gaussian-distributed random integer in <code class="literal">[lb, ub]</code>,
see below</td><td><code class="literal">random_gaussian(1, 10, 2.5)</code></td><td>an integer between <code class="literal">1</code> and <code class="literal">10</code></td></tr><tr><td><code class="literal"><code class="function">random_zipfian(<em class="replaceable"><code>lb</code></em>, <em class="replaceable"><code>ub</code></em>, <em class="replaceable"><code>parameter</code></em>)</code></code></td><td>integer</td><td>Zipfian-distributed random integer in <code class="literal">[lb, ub]</code>,
see below</td><td><code class="literal">random_zipfian(1, 10, 1.5)</code></td><td>an integer between <code class="literal">1</code> and <code class="literal">10</code></td></tr><tr><td><code class="literal"><code class="function">sqrt(<em class="replaceable"><code>x</code></em>)</code></code></td><td>double</td><td>square root</td><td><code class="literal">sqrt(2.0)</code></td><td><code class="literal">1.414213562</code></td></tr></tbody></table></div></div><br class="table-break" /><p>
The <code class="literal">random</code> function generates values using a uniform
distribution, that is all the values are drawn within the specified
range with equal probability. The <code class="literal">random_exponential</code>,
<code class="literal">random_gaussian</code> and <code class="literal">random_zipfian</code>
functions require an additional double parameter which determines the precise
shape of the distribution.
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
For an exponential distribution, <em class="replaceable"><code>parameter</code></em>
controls the distribution by truncating a quickly-decreasing
exponential distribution at <em class="replaceable"><code>parameter</code></em>, and then
projecting onto integers between the bounds.
To be precise, with
</p><div class="literallayout"><p><br />
f(x) = exp(-parameter * (x - min) / (max - min + 1)) / (1 - exp(-parameter))<br />
</p></div><p>
Then value <em class="replaceable"><code>i</code></em> between <em class="replaceable"><code>min</code></em> and
<em class="replaceable"><code>max</code></em> inclusive is drawn with probability:
<code class="literal">f(i) - f(i + 1)</code>.
</p><p>
Intuitively, the larger the <em class="replaceable"><code>parameter</code></em>, the more
frequently values close to <em class="replaceable"><code>min</code></em> are accessed, and the
less frequently values close to <em class="replaceable"><code>max</code></em> are accessed.
The closer to 0 <em class="replaceable"><code>parameter</code></em> 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 <em class="replaceable"><code>min</code></em>, are drawn
<em class="replaceable"><code>parameter</code></em>% of the time.
The <em class="replaceable"><code>parameter</code></em> value must be strictly positive.
</p></li><li class="listitem"><p>
For a Gaussian distribution, the interval is mapped onto a standard
normal distribution (the classical bell-shaped Gaussian curve) truncated
at <code class="literal">-parameter</code> on the left and <code class="literal">+parameter</code>
on the right.
Values in the middle of the interval are more likely to be drawn.
To be precise, if <code class="literal">PHI(x)</code> is the cumulative distribution
function of the standard normal distribution, with mean <code class="literal">mu</code>
defined as <code class="literal">(max + min) / 2.0</code>, with
</p><div class="literallayout"><p><br />
f(x) = PHI(2.0 * parameter * (x - mu) / (max - min + 1)) /<br />
(2.0 * PHI(parameter) - 1)<br />
</p></div><p>
then value <em class="replaceable"><code>i</code></em> between <em class="replaceable"><code>min</code></em> and
<em class="replaceable"><code>max</code></em> inclusive is drawn with probability:
<code class="literal">f(i + 0.5) - f(i - 0.5)</code>.
Intuitively, the larger the <em class="replaceable"><code>parameter</code></em>, the more
frequently values close to the middle of the interval are drawn, and the
less frequently values close to the <em class="replaceable"><code>min</code></em> and
<em class="replaceable"><code>max</code></em> bounds. About 67% of values are drawn from the
middle <code class="literal">1.0 / parameter</code>, that is a relative
<code class="literal">0.5 / parameter</code> around the mean, and 95% in the middle
<code class="literal">2.0 / parameter</code>, that is a relative
<code class="literal">1.0 / parameter</code> around the mean; for instance, if
<em class="replaceable"><code>parameter</code></em> is 4.0, 67% of values are drawn from the
middle quarter (1.0 / 4.0) of the interval (i.e. from
<code class="literal">3.0 / 8.0</code> to <code class="literal">5.0 / 8.0</code>) and 95% from
the middle half (<code class="literal">2.0 / 4.0</code>) of the interval (second and third
quartiles). The minimum <em class="replaceable"><code>parameter</code></em> is 2.0 for performance
of the Box-Muller transform.
</p></li><li class="listitem"><p>
<code class="literal">random_zipfian</code> generates an approximated bounded Zipfian
distribution. For <em class="replaceable"><code>parameter</code></em> in (0, 1), an
approximated algorithm is taken from
"Quickly Generating Billion-Record Synthetic Databases",
Jim Gray et al, SIGMOD 1994. For <em class="replaceable"><code>parameter</code></em>
in (1, 1000), a rejection method is used, based on
"Non-Uniform Random Variate Generation", Luc Devroye, p. 550-551,
Springer 1986. The distribution is not defined when the parameter's
value is 1.0. The function's performance is poor for parameter values
close and above 1.0 and on a small range.
</p><p>
<em class="replaceable"><code>parameter</code></em> defines how skewed the distribution
is. The larger the <em class="replaceable"><code>parameter</code></em>, the more
frequently values closer to the beginning of the interval are drawn.
The closer to 0 <em class="replaceable"><code>parameter</code></em> is,
the flatter (more uniform) the output distribution.
The distribution is such that, assuming the range starts from 1,
the ratio of the probability of drawing <em class="replaceable"><code>k</code></em>
versus drawing <em class="replaceable"><code>k+1</code></em> is
<code class="literal">((<em class="replaceable"><code>k</code></em>+1)/<em class="replaceable"><code>k</code></em>)**<em class="replaceable"><code>parameter</code></em></code>.
For example, <code class="literal">random_zipfian(1, ..., 2.5)</code> produces
the value <code class="literal">1</code> about <code class="literal">(2/1)**2.5 =
5.66</code> times more frequently than <code class="literal">2</code>, which
itself is produced <code class="literal">(3/2)**2.5 = 2.76</code> times more
frequently than <code class="literal">3</code>, and so on.
</p></li></ul></div><p>
Hash functions <code class="literal">hash</code>, <code class="literal">hash_murmur2</code> and
<code class="literal">hash_fnv1a</code> accept an input value and an optional seed parameter.
In case the seed isn't provided the value of <code class="literal">:default_seed</code>
is used, which is initialized randomly unless set by the command-line
<code class="literal">-D</code> option. Hash functions can be used to scatter the
distribution of random functions such as <code class="literal">random_zipfian</code> or
<code class="literal">random_exponential</code>. For instance, the following pgbench
script simulates possible real world workload typical for social media and
blogging platforms where few accounts generate excessive load:
</p><pre class="programlisting">
\set r random_zipfian(0, 100000000, 1.07)
\set k abs(hash(:r)) % 1000000
</pre><p>
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:
</p><pre class="programlisting">
\set k1 abs(hash(:r, :default_seed + 123)) % 1000000
\set k2 abs(hash(:r, :default_seed + 321)) % 1000000
</pre><p>
</p><p>
As an example, the full definition of the built-in TPC-B-like
transaction is:
</p><pre class="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;
</pre><p>
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.)
</p></div><div class="refsect2" id="id-1.9.4.10.7.6"><h3>Per-Transaction Logging</h3><p>
With the <code class="option">-l</code> option (but without
the <code class="option">--aggregate-interval</code> option),
<span class="application">pgbench</span> writes information about each transaction
to a log file. The log file will be named
<code class="filename"><em class="replaceable"><code>prefix</code></em>.<em class="replaceable"><code>nnn</code></em></code>,
where <em class="replaceable"><code>prefix</code></em> defaults to <code class="literal">pgbench_log</code>, and
<em class="replaceable"><code>nnn</code></em> is the PID of the
<span class="application">pgbench</span> process.
The prefix can be changed by using the <code class="option">--log-prefix</code> option.
If the <code class="option">-j</code> 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
<code class="filename"><em class="replaceable"><code>prefix</code></em>.<em class="replaceable"><code>nnn</code></em>.<em class="replaceable"><code>mmm</code></em></code>,
where <em class="replaceable"><code>mmm</code></em> is a sequential number for each worker starting
with 1.
</p><p>
The format of the log is:
</p><pre class="synopsis">
<em class="replaceable"><code>client_id</code></em> <em class="replaceable"><code>transaction_no</code></em> <em class="replaceable"><code>time</code></em> <em class="replaceable"><code>script_no</code></em> <em class="replaceable"><code>time_epoch</code></em> <em class="replaceable"><code>time_us</code></em> [<span class="optional"> <em class="replaceable"><code>schedule_lag</code></em> </span>]
</pre><p>
where
<em class="replaceable"><code>client_id</code></em> indicates which client session ran the transaction,
<em class="replaceable"><code>transaction_no</code></em> counts how many transactions have been
run by that session,
<em class="replaceable"><code>time</code></em> is the total elapsed transaction time in microseconds,
<em class="replaceable"><code>script_no</code></em> identifies which script file was used (useful when
multiple scripts were specified with <code class="option">-f</code> or <code class="option">-b</code>),
and <em class="replaceable"><code>time_epoch</code></em>/<em class="replaceable"><code>time_us</code></em> 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 <em class="replaceable"><code>schedule_lag</code></em> 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 <code class="option">--rate</code> option is used.
When both <code class="option">--rate</code> and <code class="option">--latency-limit</code> are used,
the <em class="replaceable"><code>time</code></em> for a skipped transaction will be reported as
<code class="literal">skipped</code>.
</p><p>
Here is a snippet of a log file generated in a single-client run:
</p><pre class="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
</pre><p>
Another example with <code class="literal">--rate=100</code>
and <code class="literal">--latency-limit=5</code> (note the additional
<em class="replaceable"><code>schedule_lag</code></em> column):
</p><pre class="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
</pre><p>
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.
</p><p>
When running a long test on hardware that can handle a lot of transactions,
the log files can become very large. The <code class="option">--sampling-rate</code> option
can be used to log only a random sample of transactions.
</p></div><div class="refsect2" id="id-1.9.4.10.7.7"><h3>Aggregated Logging</h3><p>
With the <code class="option">--aggregate-interval</code> option, a different
format is used for the log files:
</p><pre class="synopsis">
<em class="replaceable"><code>interval_start</code></em> <em class="replaceable"><code>num_transactions</code></em> <em class="replaceable"><code>sum_latency</code></em> <em class="replaceable"><code>sum_latency_2</code></em> <em class="replaceable"><code>min_latency</code></em> <em class="replaceable"><code>max_latency</code></em> [<span class="optional"> <em class="replaceable"><code>sum_lag</code></em> <em class="replaceable"><code>sum_lag_2</code></em> <em class="replaceable"><code>min_lag</code></em> <em class="replaceable"><code>max_lag</code></em> [<span class="optional"> <em class="replaceable"><code>skipped</code></em> </span>] </span>]
</pre><p>
where
<em class="replaceable"><code>interval_start</code></em> is the start of the interval (as a Unix
epoch time stamp),
<em class="replaceable"><code>num_transactions</code></em> is the number of transactions
within the interval,
<em class="replaceable"><code>sum_latency</code></em> is the sum of the transaction
latencies within the interval,
<em class="replaceable"><code>sum_latency_2</code></em> is the sum of squares of the
transaction latencies within the interval,
<em class="replaceable"><code>min_latency</code></em> is the minimum latency within the interval,
and
<em class="replaceable"><code>max_latency</code></em> is the maximum latency within the interval.
The next fields,
<em class="replaceable"><code>sum_lag</code></em>, <em class="replaceable"><code>sum_lag_2</code></em>, <em class="replaceable"><code>min_lag</code></em>,
and <em class="replaceable"><code>max_lag</code></em>, are only present if the <code class="option">--rate</code>
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, <em class="replaceable"><code>skipped</code></em>,
is only present if the <code class="option">--latency-limit</code> 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.
</p><p>
Here is some example output:
</p><pre class="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
</pre><p>
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.
</p></div><div class="refsect2" id="id-1.9.4.10.7.8"><h3>Per-Statement Latencies</h3><p>
With the <code class="option">-r</code> option, <span class="application">pgbench</span> 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.
</p><p>
For the default script, the output will look similar to this:
</p><pre class="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;
</pre><p>
</p><p>
If multiple script files are specified, the averages are reported
separately for each script file.
</p><p>
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.
</p></div><div class="refsect2" id="id-1.9.4.10.7.9"><h3>Good Practices</h3><p>
It is very easy to use <span class="application">pgbench</span> to produce completely
meaningless numbers. Here are some guidelines to help you get useful
results.
</p><p>
In the first place, <span class="emphasis"><em>never</em></span> believe any test that runs
for only a few seconds. Use the <code class="option">-t</code> or <code class="option">-T</code> 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.
</p><p>
For the default TPC-B-like test scenario, the initialization scale factor
(<code class="option">-s</code>) should be at least as large as the largest number of
clients you intend to test (<code class="option">-c</code>); else you'll mostly be
measuring update contention. There are only <code class="option">-s</code> rows in
the <code class="structname">pgbench_branches</code> table, and every transaction wants to
update one of them, so <code class="option">-c</code> values in excess of <code class="option">-s</code>
will undoubtedly result in lots of transactions blocked waiting for
other transactions.
</p><p>
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.
</p><p>
A limitation of <span class="application">pgbench</span> is that it can itself become
the bottleneck when trying to test a large number of client sessions.
This can be alleviated by running <span class="application">pgbench</span> on a different
machine from the database server, although low network latency will be
essential. It might even be useful to run several <span class="application">pgbench</span>
instances concurrently, on several client machines, against the same
database server.
</p></div><div class="refsect2" id="id-1.9.4.10.7.10"><h3>Security</h3><p>
If untrusted users have access to a database that has not adopted a
<a class="link" href="ddl-schemas.html#DDL-SCHEMAS-PATTERNS" title="5.8.6. Usage Patterns">secure schema usage pattern</a>,
do not run <span class="application">pgbench</span> in that
database. <span class="application">pgbench</span> uses unqualified names and
does not manipulate the search path.
</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="app-pgbasebackup.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="reference-client.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="app-pgconfig.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">pg_basebackup </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> pg_config</td></tr></table></div></body></html>
