Unix/Linux Go Back    


CentOS 7.0 - man page for pgbench (centos section 1)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)


PGBENCH(1)			  PostgreSQL 9.2.7 Documentation		       PGBENCH(1)

NAME
       pgbench - run a benchmark test on PostgreSQL

SYNOPSIS
       pgbench -i [option...] [dbname]

       pgbench [option...] [dbname]

DESCRIPTION
       pgbench is a simple program for running benchmark tests on PostgreSQL. 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,
       pgbench tests a scenario that is loosely based on TPC-B, involving five SELECT, UPDATE,
       and INSERT commands per transaction. However, it is easy to test other cases by writing
       your own transaction script files.

       Typical output from pgbench looks like:

	   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)

       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 -T 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.

       The default TPC-B-like transaction test requires specific tables to be set up beforehand.
       pgbench should be invoked with the -i (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:

	   pgbench -i [ other-options ] dbname

       where dbname is the name of the already-created database to test in. (You may also need
       -h, -p, and/or -U options to specify how to connect to the database server.)

	   Caution
	   pgbench -i creates four tables pgbench_accounts, pgbench_branches, pgbench_history,
	   and pgbench_tellers, destroying any existing tables of these names. Be very careful to
	   use another database if you have tables having these names!

       At the default "scale factor" of 1, the tables initially contain this many rows:

	   table		   # of rows
	   ---------------------------------
	   pgbench_branches	   1
	   pgbench_tellers	   10
	   pgbench_accounts	   100000
	   pgbench_history	   0

       You can (and, for most purposes, probably should) increase the number of rows by using the
       -s (scale factor) option. The -F (fillfactor) option might also be used at this point.

       Once you have done the necessary setup, you can run your benchmark with a command that
       doesn't include -i, that is

	   pgbench [ options ] dbname

       In nearly all cases, you'll need some options to make a useful test. The most important
       options are -c (number of clients), -t (number of transactions), -T (time limit), and -f
       (specify a custom script file). See below for a full list.

OPTIONS
       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.

   Initialization Options
       pgbench accepts the following command-line initialization arguments:

       -i
	   Required to invoke initialization mode.

       -F fillfactor
	   Create the pgbench_accounts, pgbench_tellers and pgbench_branches tables with the
	   given fillfactor. Default is 100.

       -s scale_factor
	   Multiply the number of rows generated by the scale factor. For example, -s 100 will
	   create 10,000,000 rows in the pgbench_accounts table. Default is 1.

       --index-tablespace=index_tablespace
	   Create indexes in the specified tablespace, rather than the default tablespace.

       --tablespace=tablespace
	   Create tables in the specified tablespace, rather than the default tablespace.

       --unlogged-tables
	   Create all tables as unlogged tables, rather than permanent tables.

   Benchmarking Options
       pgbench accepts the following command-line benchmarking arguments:

       -c clients
	   Number of clients simulated, that is, number of concurrent database sessions. Default
	   is 1.

       -C
	   Establish a new connection for each transaction, rather than doing it just once per
	   client session. This is useful to measure the connection overhead.

       -d
	   Print debugging output.

       -D varname=value
	   Define a variable for use by a custom script (see below). Multiple -D options are
	   allowed.

       -f filename
	   Read transaction script from filename. See below for details.  -N, -S, and -f are
	   mutually exclusive.

       -j threads
	   Number of worker threads within pgbench. 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.

       -l
	   Write the time taken by each transaction to a log file. See below for details.

       -M querymode
	   Protocol to use for submitting queries to the server:

	   o   simple: use simple query protocol.

	   o   extended: use extended query protocol.

	   o   prepared: use extended query protocol with prepared statements.

	   The default is simple query protocol. (See Chapter 46, Frontend/Backend Protocol, in
	   the documentation for more information.)

       -n
	   Perform no vacuuming before running the test. This option is necessary if you are
	   running a custom test scenario that does not include the standard tables
	   pgbench_accounts, pgbench_branches, pgbench_history, and pgbench_tellers.

       -N
	   Do not update pgbench_tellers and pgbench_branches. This will avoid update contention
	   on these tables, but it makes the test case even less like TPC-B.

       -r
	   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.

       -s scale_factor
	   Report the specified scale factor in pgbench'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 pgbench_branches table. However, when testing custom benchmarks (-f
	   option), the scale factor will be reported as 1 unless this option is used.

       -S
	   Perform select-only transactions instead of TPC-B-like test.

       -t transactions
	   Number of transactions each client runs. Default is 10.

       -T seconds
	   Run the test for this many seconds, rather than a fixed number of transactions per
	   client.  -t and -T are mutually exclusive.

       -v
	   Vacuum all four standard tables before running the test. With neither -n nor -v,
	   pgbench will vacuum the pgbench_tellers and pgbench_branches tables, and will truncate
	   pgbench_history.

   Common Options
       pgbench accepts the following command-line common arguments:

       -h hostname
	   The database server's host name

       -p port
	   The database server's port number

       -U login
	   The user name to connect as

       -V, --version
	   Print the pgbench version and exit.

       -?, --help
	   Show help about pgbench command line arguments, and exit.

NOTES
   What is the "Transaction" Actually Performed in pgbench?
       The default transaction script issues seven commands per transaction:

	1. BEGIN;

	2. UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;

	3. SELECT abalance FROM pgbench_accounts WHERE aid = :aid;

	4. UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;

	5. UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;

	6. INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid,
	   :delta, CURRENT_TIMESTAMP);

	7. END;

       If you specify -N, steps 4 and 5 aren't included in the transaction. If you specify -S,
       only the SELECT is issued.

   Custom Scripts
       pgbench has support for running custom benchmark scenarios by replacing the default
       transaction script (described above) with a transaction script read from a file (-f
       option). In this case a "transaction" counts as one execution of a script file. You can
       even specify multiple scripts (multiple -f options), in which case a random one of the
       scripts is chosen each time a client session starts a new transaction.

       The format of a script file is one SQL command per line; multiline SQL commands are not
       supported. Empty lines and lines beginning with -- are ignored. Script file lines can also
       be "meta commands", which are interpreted by pgbench itself, as described below.

       There is a simple variable-substitution facility for script files. Variables can be set by
       the command-line -D option, explained above, or by the meta commands explained below. In
       addition to any variables preset by -D command-line options, the variable scale is preset
       to the current scale factor. Once set, a variable's value can be inserted into a SQL
       command by writing :variablename. When running more than one client session, each session
       has its own set of variables.

       Script file meta commands begin with a backslash (\). Arguments to a meta command are
       separated by white space. These meta commands are supported:

       \set varname operand1 [ operator operand2 ]
	   Sets variable varname to a calculated integer value. Each operand is either an integer
	   constant or a :variablename reference to a variable having an integer value. The
	   operator can be +, -, *, or /.

	   Example:

	       \set ntellers 10 * :scale

       \setrandom varname min max
	   Sets variable varname to a random integer value between the limits min and max
	   inclusive. Each limit can be either an integer constant or a :variablename reference
	   to a variable having an integer value.

	   Example:

	       \setrandom aid 1 :naccounts

       \sleep number [ us | ms | s ]
	   Causes script execution to sleep for the specified duration in microseconds (us),
	   milliseconds (ms) or seconds (s). If the unit is omitted then seconds are the default.
	   number can be either an integer constant or a :variablename reference to a variable
	   having an integer value.

	   Example:

	       \sleep 10 ms

       \setshell varname command [ argument ... ]
	   Sets variable varname to the result of the shell command command. The command must
	   return an integer value through its standard output.

	   argument can be either a text constant or a :variablename reference to a variable of
	   any types. If you want to use argument starting with colons, you need to add an
	   additional colon at the beginning of argument.

	   Example:

	       \setshell variable_to_be_assigned command literal_argument :variable ::literal_starting_with_colon

       \shell command [ argument ... ]
	   Same as \setshell, but the result is ignored.

	   Example:

	       \shell command literal_argument :variable ::literal_starting_with_colon

       As an example, the full definition of the built-in TPC-B-like transaction is:

	   \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;

       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.)

   Per-Transaction Logging
       With the -l option, pgbench writes the time taken by each transaction to a log file. The
       log file will be named pgbench_log.nnn, where nnn is the PID of the pgbench process. If
       the -j 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
       pgbench_log.nnn.mmm, where mmm is a sequential number for each worker starting with 1.

       The format of the log is:

	   client_id transaction_no time file_no time_epoch time_us

       where time is the total elapsed transaction time in microseconds, file_no identifies which
       script file was used (useful when multiple scripts were specified with -f), and
       time_epoch/time_us are a UNIX epoch format timestamp and an offset in microseconds
       (suitable for creating a ISO 8601 timestamp with fractional seconds) showing when the
       transaction completed.

       Here are example outputs:

	    0 199 2241 0 1175850568 995598
	    0 200 2465 0 1175850568 998079
	    0 201 2513 0 1175850569 608
	    0 202 2038 0 1175850569 2663

   Per-Statement Latencies
       With the -r option, pgbench 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.

       For the default script, the output will look similar to this:

	   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;

       If multiple script files are specified, the averages are reported separately for each
       script file.

       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.

   Good Practices
       It is very easy to use pgbench to produce completely meaningless numbers. Here are some
       guidelines to help you get useful results.

       In the first place, never believe any test that runs for only a few seconds. Use the -t or
       -T 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.

       For the default TPC-B-like test scenario, the initialization scale factor (-s) should be
       at least as large as the largest number of clients you intend to test (-c); else you'll
       mostly be measuring update contention. There are only -s rows in the pgbench_branches
       table, and every transaction wants to update one of them, so -c values in excess of -s
       will undoubtedly result in lots of transactions blocked waiting for other transactions.

       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.

       A limitation of pgbench is that it can itself become the bottleneck when trying to test a
       large number of client sessions. This can be alleviated by running pgbench on a different
       machine from the database server, although low network latency will be essential. It might
       even be useful to run several pgbench instances concurrently, on several client machines,
       against the same database server.

PostgreSQL 9.2.7			    2014-02-17				       PGBENCH(1)
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums


All times are GMT -4. The time now is 04:27 PM.