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><H1
><A
NAME="PGBENCH"
></A
><SPAN
CLASS="APPLICATION"
>pgbench</SPAN
></H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN153217"
></A
><H2
>Name</H2
>pgbench -- run a benchmark test on <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
></DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN153223"
></A
><H2
>Synopsis</H2
><P
><TT
CLASS="COMMAND"
>pgbench</TT
> <TT
CLASS="OPTION"
>-i</TT
> [<TT
CLASS="REPLACEABLE"
><I
>option</I
></TT
>...] [<TT
CLASS="REPLACEABLE"
><I
>dbname</I
></TT
>]</P
><P
><TT
CLASS="COMMAND"
>pgbench</TT
> [<TT
CLASS="REPLACEABLE"
><I
>option</I
></TT
>...] [<TT
CLASS="REPLACEABLE"
><I
>dbname</I
></TT
>]</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN153238"
></A
><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 <TT
CLASS="COMMAND"
>SELECT</TT
>,
<TT
CLASS="COMMAND"
>UPDATE</TT
>, and <TT
CLASS="COMMAND"
>INSERT</TT
> commands per transaction.
However, it is easy to test other cases by writing your own transaction
script files.
</P
><P
> Typical output from pgbench looks like:
</P><PRE
CLASS="SCREEN"
>transaction type: 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 <TT
CLASS="OPTION"
>-T</TT
> 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 <TT
CLASS="OPTION"
>-i</TT
> (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"
> <TT
CLASS="REPLACEABLE"
><I
>other-options</I
></TT
> </SPAN
>] <TT
CLASS="REPLACEABLE"
><I
>dbname</I
></TT
></PRE
><P>
where <TT
CLASS="REPLACEABLE"
><I
>dbname</I
></TT
> is the name of the already-created
database to test in. (You may also need <TT
CLASS="OPTION"
>-h</TT
>,
<TT
CLASS="OPTION"
>-p</TT
>, and/or <TT
CLASS="OPTION"
>-U</TT
> options to specify how to
connect to the database server.)
</P
><DIV
CLASS="CAUTION"
><P
></P
><TABLE
CLASS="CAUTION"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Caution</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
> <TT
CLASS="LITERAL"
>pgbench -i</TT
> creates four tables <TT
CLASS="STRUCTNAME"
>pgbench_accounts</TT
>,
<TT
CLASS="STRUCTNAME"
>pgbench_branches</TT
>, <TT
CLASS="STRUCTNAME"
>pgbench_history</TT
>, and
<TT
CLASS="STRUCTNAME"
>pgbench_tellers</TT
>,
destroying any existing tables of these names.
Be very careful to use another database if you have tables having these
names!
</P
></TD
></TR
></TABLE
></DIV
><P
> At the default <SPAN
CLASS="QUOTE"
>"scale factor"</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 <TT
CLASS="OPTION"
>-s</TT
> (scale factor) option. The
<TT
CLASS="OPTION"
>-F</TT
> (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 <TT
CLASS="OPTION"
>-i</TT
>, that is
</P><PRE
CLASS="PROGRAMLISTING"
>pgbench [<SPAN
CLASS="OPTIONAL"
> <TT
CLASS="REPLACEABLE"
><I
>options</I
></TT
> </SPAN
>] <TT
CLASS="REPLACEABLE"
><I
>dbname</I
></TT
></PRE
><P>
In nearly all cases, you'll need some options to make a useful test.
The most important options are <TT
CLASS="OPTION"
>-c</TT
> (number of clients),
<TT
CLASS="OPTION"
>-t</TT
> (number of transactions), <TT
CLASS="OPTION"
>-T</TT
> (time limit),
and <TT
CLASS="OPTION"
>-f</TT
> (specify a custom script file).
See below for a full list.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN153283"
></A
><H2
>Options</H2
><P
> The following is divided into three subsections: Different options are used
during database initialization and while running benchmarks, some options
are useful in both cases.
</P
><DIV
CLASS="REFSECT2"
><A
NAME="PGBENCH-INIT-OPTIONS"
></A
><H3
>Initialization Options</H3
><P
> <SPAN
CLASS="APPLICATION"
>pgbench</SPAN
> accepts the following command-line
initialization arguments:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="OPTION"
>-i</TT
></DT
><DD
><P
> Required to invoke initialization mode.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-F</TT
> <TT
CLASS="REPLACEABLE"
><I
>fillfactor</I
></TT
></DT
><DD
><P
> Create the <TT
CLASS="STRUCTNAME"
>pgbench_accounts</TT
>,
<TT
CLASS="STRUCTNAME"
>pgbench_tellers</TT
> and
<TT
CLASS="STRUCTNAME"
>pgbench_branches</TT
> tables with the given fillfactor.
Default is 100.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-s</TT
> <TT
CLASS="REPLACEABLE"
><I
>scale_factor</I
></TT
></DT
><DD
><P
> Multiply the number of rows generated by the scale factor.
For example, <TT
CLASS="LITERAL"
>-s 100</TT
> will create 10,000,000 rows
in the <TT
CLASS="STRUCTNAME"
>pgbench_accounts</TT
> table. Default is 1.
</P
></DD
><DT
><TT
CLASS="OPTION"
>--index-tablespace=<TT
CLASS="REPLACEABLE"
><I
>index_tablespace</I
></TT
></TT
></DT
><DD
><P
> Create indexes in the specified tablespace, rather than the default
tablespace.
</P
></DD
><DT
><TT
CLASS="OPTION"
>--tablespace=<TT
CLASS="REPLACEABLE"
><I
>tablespace</I
></TT
></TT
></DT
><DD
><P
> Create tables in the specified tablespace, rather than the default
tablespace.
</P
></DD
><DT
><TT
CLASS="OPTION"
>--unlogged-tables</TT
></DT
><DD
><P
> Create all tables as unlogged tables, rather than permanent tables.
</P
></DD
></DL
></DIV
><P>
</P
></DIV
><DIV
CLASS="REFSECT2"
><A
NAME="PGBENCH-RUN-OPTIONS"
></A
><H3
>Benchmarking Options</H3
><P
> <SPAN
CLASS="APPLICATION"
>pgbench</SPAN
> accepts the following command-line
benchmarking arguments:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="OPTION"
>-c</TT
> <TT
CLASS="REPLACEABLE"
><I
>clients</I
></TT
></DT
><DD
><P
> Number of clients simulated, that is, number of concurrent database
sessions. Default is 1.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-C</TT
></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
><TT
CLASS="OPTION"
>-d</TT
></DT
><DD
><P
> Print debugging output.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-D</TT
> <TT
CLASS="REPLACEABLE"
><I
>varname</I
></TT
><TT
CLASS="LITERAL"
>=</TT
><TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
></DT
><DD
><P
> Define a variable for use by a custom script (see below).
Multiple <TT
CLASS="OPTION"
>-D</TT
> options are allowed.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-f</TT
> <TT
CLASS="REPLACEABLE"
><I
>filename</I
></TT
></DT
><DD
><P
> Read transaction script from <TT
CLASS="REPLACEABLE"
><I
>filename</I
></TT
>.
See below for details.
<TT
CLASS="OPTION"
>-N</TT
>, <TT
CLASS="OPTION"
>-S</TT
>, and <TT
CLASS="OPTION"
>-f</TT
>
are mutually exclusive.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-j</TT
> <TT
CLASS="REPLACEABLE"
><I
>threads</I
></TT
></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.
The number of clients must be a multiple of the number of threads,
since each thread is given the same number of client sessions to manage.
Default is 1.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-l</TT
></DT
><DD
><P
> Write the time taken by each transaction to a log file.
See below for details.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-M</TT
> <TT
CLASS="REPLACEABLE"
><I
>querymode</I
></TT
></DT
><DD
><P
> Protocol to use for submitting queries to the server:
<P
></P
></P><UL
><LI
><P
><TT
CLASS="LITERAL"
>simple</TT
>: use simple query protocol.</P
></LI
><LI
><P
><TT
CLASS="LITERAL"
>extended</TT
>: use extended query protocol.</P
></LI
><LI
><P
><TT
CLASS="LITERAL"
>prepared</TT
>: use extended query protocol with prepared statements.</P
></LI
></UL
><P>
The default is simple query protocol. (See <A
HREF="protocol.html"
>Chapter 46</A
>
for more information.)
</P
></DD
><DT
><TT
CLASS="OPTION"
>-n</TT
></DT
><DD
><P
> Perform no vacuuming before running the test.
This option is <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>necessary</I
></SPAN
>
if you are running a custom test scenario that does not include
the standard tables <TT
CLASS="STRUCTNAME"
>pgbench_accounts</TT
>,
<TT
CLASS="STRUCTNAME"
>pgbench_branches</TT
>, <TT
CLASS="STRUCTNAME"
>pgbench_history</TT
>, and
<TT
CLASS="STRUCTNAME"
>pgbench_tellers</TT
>.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-N</TT
></DT
><DD
><P
> Do not update <TT
CLASS="STRUCTNAME"
>pgbench_tellers</TT
> and
<TT
CLASS="STRUCTNAME"
>pgbench_branches</TT
>.
This will avoid update contention on these tables, but
it makes the test case even less like TPC-B.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-r</TT
></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
><TT
CLASS="OPTION"
>-s</TT
> <TT
CLASS="REPLACEABLE"
><I
>scale_factor</I
></TT
></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 <TT
CLASS="STRUCTNAME"
>pgbench_branches</TT
> table. However, when testing
custom benchmarks (<TT
CLASS="OPTION"
>-f</TT
> option), the scale factor
will be reported as 1 unless this option is used.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-S</TT
></DT
><DD
><P
> Perform select-only transactions instead of TPC-B-like test.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-t</TT
> <TT
CLASS="REPLACEABLE"
><I
>transactions</I
></TT
></DT
><DD
><P
> Number of transactions each client runs. Default is 10.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-T</TT
> <TT
CLASS="REPLACEABLE"
><I
>seconds</I
></TT
></DT
><DD
><P
> Run the test for this many seconds, rather than a fixed number of
transactions per client. <TT
CLASS="OPTION"
>-t</TT
> and
<TT
CLASS="OPTION"
>-T</TT
> are mutually exclusive.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-v</TT
></DT
><DD
><P
> Vacuum all four standard tables before running the test.
With neither <TT
CLASS="OPTION"
>-n</TT
> nor <TT
CLASS="OPTION"
>-v</TT
>, pgbench will vacuum the
<TT
CLASS="STRUCTNAME"
>pgbench_tellers</TT
> and <TT
CLASS="STRUCTNAME"
>pgbench_branches</TT
>
tables, and will truncate <TT
CLASS="STRUCTNAME"
>pgbench_history</TT
>.
</P
></DD
></DL
></DIV
><P>
</P
></DIV
><DIV
CLASS="REFSECT2"
><A
NAME="PGBENCH-COMMON-OPTIONS"
></A
><H3
>Common Options</H3
><P
> <SPAN
CLASS="APPLICATION"
>pgbench</SPAN
> accepts the following command-line
common arguments:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="OPTION"
>-h</TT
> <TT
CLASS="REPLACEABLE"
><I
>hostname</I
></TT
></DT
><DD
><P
> The database server's host name
</P
></DD
><DT
><TT
CLASS="OPTION"
>-p</TT
> <TT
CLASS="REPLACEABLE"
><I
>port</I
></TT
></DT
><DD
><P
> The database server's port number
</P
></DD
><DT
><TT
CLASS="OPTION"
>-U</TT
> <TT
CLASS="REPLACEABLE"
><I
>login</I
></TT
></DT
><DD
><P
> The user name to connect as
</P
></DD
><DT
><TT
CLASS="OPTION"
>-V</TT
><BR><TT
CLASS="OPTION"
>--version</TT
></DT
><DD
><P
> Print the <SPAN
CLASS="APPLICATION"
>pgbench</SPAN
> version and exit.
</P
></DD
><DT
><TT
CLASS="OPTION"
>-?</TT
><BR><TT
CLASS="OPTION"
>--help</TT
></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"
><A
NAME="AEN153498"
></A
><H2
>Notes</H2
><DIV
CLASS="REFSECT2"
><A
NAME="AEN153500"
></A
><H3
>What is the <SPAN
CLASS="QUOTE"
>"Transaction"</SPAN
> Actually Performed in pgbench?</H3
><P
> The default transaction script issues seven commands per transaction:
</P
><P
></P
><OL
TYPE="1"
><LI
><P
><TT
CLASS="LITERAL"
>BEGIN;</TT
></P
></LI
><LI
><P
><TT
CLASS="LITERAL"
>UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;</TT
></P
></LI
><LI
><P
><TT
CLASS="LITERAL"
>SELECT abalance FROM pgbench_accounts WHERE aid = :aid;</TT
></P
></LI
><LI
><P
><TT
CLASS="LITERAL"
>UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;</TT
></P
></LI
><LI
><P
><TT
CLASS="LITERAL"
>UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;</TT
></P
></LI
><LI
><P
><TT
CLASS="LITERAL"
>INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);</TT
></P
></LI
><LI
><P
><TT
CLASS="LITERAL"
>END;</TT
></P
></LI
></OL
><P
> If you specify <TT
CLASS="OPTION"
>-N</TT
>, steps 4 and 5 aren't included in the
transaction. If you specify <TT
CLASS="OPTION"
>-S</TT
>, only the <TT
CLASS="COMMAND"
>SELECT</TT
> is
issued.
</P
></DIV
><DIV
CLASS="REFSECT2"
><A
NAME="AEN153530"
></A
><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
(<TT
CLASS="OPTION"
>-f</TT
> option). In this case a <SPAN
CLASS="QUOTE"
>"transaction"</SPAN
>
counts as one execution of a script file. You can even specify
multiple scripts (multiple <TT
CLASS="OPTION"
>-f</TT
> options), in which
case a random one of the scripts is chosen each time a client session
starts a new transaction.
</P
><P
> The format of a script file is one SQL command per line; multiline
SQL commands are not supported. Empty lines and lines beginning with
<TT
CLASS="LITERAL"
>--</TT
> are ignored. Script file lines can also be
<SPAN
CLASS="QUOTE"
>"meta commands"</SPAN
>, which are interpreted by <SPAN
CLASS="APPLICATION"
>pgbench</SPAN
>
itself, as described below.
</P
><P
> There is a simple variable-substitution facility for script files.
Variables can be set by the command-line <TT
CLASS="OPTION"
>-D</TT
> option,
explained above, or by the meta commands explained below.
In addition to any variables preset by <TT
CLASS="OPTION"
>-D</TT
> command-line options,
the variable <TT
CLASS="LITERAL"
>scale</TT
> is preset to the current scale factor.
Once set, a variable's
value can be inserted into a SQL command by writing
<TT
CLASS="LITERAL"
>:</TT
><TT
CLASS="REPLACEABLE"
><I
>variablename</I
></TT
>. When running more than
one client session, each session has its own set of variables.
</P
><P
> Script file meta commands begin with a backslash (<TT
CLASS="LITERAL"
>\</TT
>).
Arguments to a meta command are separated by white space.
These meta commands are supported:
</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>\set <TT
CLASS="REPLACEABLE"
><I
>varname</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>operand1</I
></TT
> [ <TT
CLASS="REPLACEABLE"
><I
>operator</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>operand2</I
></TT
> ]</TT
></DT
><DD
><P
> Sets variable <TT
CLASS="REPLACEABLE"
><I
>varname</I
></TT
> to a calculated integer value.
Each <TT
CLASS="REPLACEABLE"
><I
>operand</I
></TT
> is either an integer constant or a
<TT
CLASS="LITERAL"
>:</TT
><TT
CLASS="REPLACEABLE"
><I
>variablename</I
></TT
> reference to a variable
having an integer value. The <TT
CLASS="REPLACEABLE"
><I
>operator</I
></TT
> can be
<TT
CLASS="LITERAL"
>+</TT
>, <TT
CLASS="LITERAL"
>-</TT
>, <TT
CLASS="LITERAL"
>*</TT
>, or <TT
CLASS="LITERAL"
>/</TT
>.
</P
><P
> Example:
</P><PRE
CLASS="PROGRAMLISTING"
>\set ntellers 10 * :scale</PRE
><P></P
></DD
><DT
><TT
CLASS="LITERAL"
>\setrandom <TT
CLASS="REPLACEABLE"
><I
>varname</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>min</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>max</I
></TT
></TT
></DT
><DD
><P
> Sets variable <TT
CLASS="REPLACEABLE"
><I
>varname</I
></TT
> to a random integer value
between the limits <TT
CLASS="REPLACEABLE"
><I
>min</I
></TT
> and <TT
CLASS="REPLACEABLE"
><I
>max</I
></TT
> inclusive.
Each limit can be either an integer constant or a
<TT
CLASS="LITERAL"
>:</TT
><TT
CLASS="REPLACEABLE"
><I
>variablename</I
></TT
> reference to a variable
having an integer value.
</P
><P
> Example:
</P><PRE
CLASS="PROGRAMLISTING"
>\setrandom aid 1 :naccounts</PRE
><P></P
></DD
><DT
><TT
CLASS="LITERAL"
>\sleep <TT
CLASS="REPLACEABLE"
><I
>number</I
></TT
> [ us | ms | s ]</TT
></DT
><DD
><P
> Causes script execution to sleep for the specified duration in
microseconds (<TT
CLASS="LITERAL"
>us</TT
>), milliseconds (<TT
CLASS="LITERAL"
>ms</TT
>) or seconds
(<TT
CLASS="LITERAL"
>s</TT
>). If the unit is omitted then seconds are the default.
<TT
CLASS="REPLACEABLE"
><I
>number</I
></TT
> can be either an integer constant or a
<TT
CLASS="LITERAL"
>:</TT
><TT
CLASS="REPLACEABLE"
><I
>variablename</I
></TT
> reference to a variable
having an integer value.
</P
><P
> Example:
</P><PRE
CLASS="PROGRAMLISTING"
>\sleep 10 ms</PRE
><P></P
></DD
><DT
><TT
CLASS="LITERAL"
>\setshell <TT
CLASS="REPLACEABLE"
><I
>varname</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>command</I
></TT
> [ <TT
CLASS="REPLACEABLE"
><I
>argument</I
></TT
> ... ]</TT
></DT
><DD
><P
> Sets variable <TT
CLASS="REPLACEABLE"
><I
>varname</I
></TT
> to the result of the shell command
<TT
CLASS="REPLACEABLE"
><I
>command</I
></TT
>. The command must return an integer value
through its standard output.
</P
><P
> <TT
CLASS="REPLACEABLE"
><I
>argument</I
></TT
> can be either a text constant or a
<TT
CLASS="LITERAL"
>:</TT
><TT
CLASS="REPLACEABLE"
><I
>variablename</I
></TT
> reference to a variable of
any types. If you want to use <TT
CLASS="REPLACEABLE"
><I
>argument</I
></TT
> starting with
colons, you need to add an additional colon at the beginning of
<TT
CLASS="REPLACEABLE"
><I
>argument</I
></TT
>.
</P
><P
> Example:
</P><PRE
CLASS="PROGRAMLISTING"
>\setshell variable_to_be_assigned command literal_argument :variable ::literal_starting_with_colon</PRE
><P></P
></DD
><DT
><TT
CLASS="LITERAL"
>\shell <TT
CLASS="REPLACEABLE"
><I
>command</I
></TT
> [ <TT
CLASS="REPLACEABLE"
><I
>argument</I
></TT
> ... ]</TT
></DT
><DD
><P
> Same as <TT
CLASS="LITERAL"
>\setshell</TT
>, but the result is ignored.
</P
><P
> Example:
</P><PRE
CLASS="PROGRAMLISTING"
>\shell command literal_argument :variable ::literal_starting_with_colon</PRE
><P></P
></DD
></DL
></DIV
><P
> As an example, the full definition of the built-in TPC-B-like
transaction is:
</P><PRE
CLASS="PROGRAMLISTING"
>\set nbranches :scale
\set ntellers 10 * :scale
\set naccounts 100000 * :scale
\setrandom aid 1 :naccounts
\setrandom bid 1 :nbranches
\setrandom tid 1 :ntellers
\setrandom delta -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"
><A
NAME="AEN153629"
></A
><H3
>Per-Transaction Logging</H3
><P
> With the <TT
CLASS="OPTION"
>-l</TT
> option, <SPAN
CLASS="APPLICATION"
>pgbench</SPAN
> writes the time
taken by each transaction to a log file. The log file will be named
<TT
CLASS="FILENAME"
>pgbench_log.<TT
CLASS="REPLACEABLE"
><I
>nnn</I
></TT
></TT
>, where
<TT
CLASS="REPLACEABLE"
><I
>nnn</I
></TT
> is the PID of the pgbench process.
If the <TT
CLASS="OPTION"
>-j</TT
> option is 2 or higher, creating 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
<TT
CLASS="FILENAME"
>pgbench_log.<TT
CLASS="REPLACEABLE"
><I
>nnn</I
></TT
>.<TT
CLASS="REPLACEABLE"
><I
>mmm</I
></TT
></TT
>,
where <TT
CLASS="REPLACEABLE"
><I
>mmm</I
></TT
> is a sequential number for each worker starting
with 1.
</P
><P
> The format of the log is:
</P><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>client_id</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>transaction_no</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>time</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>file_no</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>time_epoch</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>time_us</I
></TT
></PRE
><P>
where <TT
CLASS="REPLACEABLE"
><I
>time</I
></TT
> is the total elapsed transaction time in microseconds,
<TT
CLASS="REPLACEABLE"
><I
>file_no</I
></TT
> identifies which script file was used
(useful when multiple scripts were specified with <TT
CLASS="OPTION"
>-f</TT
>),
and <TT
CLASS="REPLACEABLE"
><I
>time_epoch</I
></TT
>/<TT
CLASS="REPLACEABLE"
><I
>time_us</I
></TT
> are a
UNIX epoch format timestamp and an offset
in microseconds (suitable for creating an ISO 8601
timestamp with fractional seconds) showing when
the transaction completed.
</P
><P
> Here are example outputs:
</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></P
></DIV
><DIV
CLASS="REFSECT2"
><A
NAME="AEN153657"
></A
><H3
>Per-Statement Latencies</H3
><P
> With the <TT
CLASS="OPTION"
>-r</TT
> 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: 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
tps = 618.764555 (including connections establishing)
tps = 622.977698 (excluding connections establishing)
statement latencies in milliseconds:
0.004386 \set nbranches 1 * :scale
0.001343 \set ntellers 10 * :scale
0.001212 \set naccounts 100000 * :scale
0.001310 \setrandom aid 1 :naccounts
0.001073 \setrandom bid 1 :nbranches
0.001005 \setrandom tid 1 :ntellers
0.001078 \setrandom delta -5000 5000
0.326152 BEGIN;
0.603376 UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;
0.454643 SELECT abalance FROM pgbench_accounts WHERE aid = :aid;
5.528491 UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;
7.335435 UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;
0.371851 INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);
1.212976 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"
><A
NAME="AEN153666"
></A
><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"
><I
CLASS="EMPHASIS"
>never</I
></SPAN
> believe any test that runs
for only a few seconds. Use the <TT
CLASS="OPTION"
>-t</TT
> or <TT
CLASS="OPTION"
>-T</TT
> 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
(<TT
CLASS="OPTION"
>-s</TT
>) should be at least as large as the largest number of
clients you intend to test (<TT
CLASS="OPTION"
>-c</TT
>); else you'll mostly be
measuring update contention. There are only <TT
CLASS="OPTION"
>-s</TT
> rows in
the <TT
CLASS="STRUCTNAME"
>pgbench_branches</TT
> table, and every transaction wants to
update one of them, so <TT
CLASS="OPTION"
>-c</TT
> values in excess of <TT
CLASS="OPTION"
>-s</TT
>
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
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