pgbench

pgbench

1

Application

pgbench

run a benchmark test on

PostgreSQL

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: <builtin: TPC-B (sort of)>
    scaling factor: 10
    query mode: simple
    number of clients: 10
    number of threads: 1
    maximum number of tries: 1
    number of transactions per client: 1000
    number of transactions actually processed: 10000/10000
    number of failed transactions: 0 (0.000%)
    latency average = 11.013 ms
    latency stddev = 7.351 ms
    initial connection time = 45.758 ms
    tps = 896.967014 (without initial connection time)

The first seven lines report some of the most important parameter
settings. The sixth line reports the maximum number of tries for
transactions with serialization or deadlock errors (see [Failures and
Serialization/Deadlock Retries](#failures-and-retries) for more
information). The eighth 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 or some SQL command(s) failed.
(In `-T` mode, only the actual number of transactions is printed.) The
next line reports the number of failed transactions due to serialization
or deadlock errors (see [Failures and Serialization/Deadlock
Retries](#failures-and-retries) for more information). The last line
reports the number of transactions per second.

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, but
some options are useful in both cases.

Initialization Options {#pgbench-init-options}
----------------------

pgbench accepts the following command-line initialization arguments:

dbname

:   Specifies the name of the database to test in. If this is not
    specified, the environment variable PGDATABASE is used. If that is
    not set, the user name specified for the connection is used.

`-i`; `--initialize`

:   Required to invoke initialization mode.

`-I init_steps`; `--init-steps=init_steps`

:   Perform just a selected set of the normal initialization steps.
    init\_steps specifies the initialization steps to be performed,
    using one character per step. Each step is invoked in the specified
    order. The default is `dtgvp`. The available steps are:

    `d` (Drop)

    :   Drop any existing pgbench tables.

    `t` (create Tables)

    :   Create the tables used by the standard pgbench scenario, namely
        pgbench\_accounts, pgbench\_branches, pgbench\_history, and
        pgbench\_tellers.

    `g` or `G` (Generate data, client-side or server-side)

    :   Generate data and load it into the standard tables, replacing
        any data already present.

        With `g` (client-side data generation), data is generated in
        `pgbench` client and then sent to the server. This uses the
        client/server bandwidth extensively through a `COPY`. `pgbench`
        uses the FREEZE option with version 14 or later of PostgreSQL to
        speed up subsequent `VACUUM`, unless partitions are enabled.
        Using `g` causes logging to print one message every 100,000 rows
        while generating data for the pgbench\_accounts table.

        With `G` (server-side data generation), only small queries are
        sent from the `pgbench` client and then data is actually
        generated in the server. No significant bandwidth is required
        for this variant, but the server will do more work. Using `G`
        causes logging not to print any progress message while
        generating data.

        The default initialization behavior uses client-side data
        generation (equivalent to `g`).

    `v` (Vacuum)

    :   Invoke `VACUUM` on the standard tables.

    `p` (create Primary keys)

    :   Create primary key indexes on the standard tables.

    `f` (create Foreign keys)

    :   Create foreign key constraints between the standard tables.
        (Note that this step is not performed by default.)

`-F` fillfactor; `--fillfactor=`fillfactor

:   Create the pgbench\_accounts, pgbench\_tellers and pgbench\_branches
    tables with the given fillfactor. Default is 100.

`-n`; `--no-vacuum`

:   Perform no vacuuming during initialization. (This option suppresses
    the `v` initialization step, even if it was specified in `-I`.)

`-q`; `--quiet`

:   Switch logging to quiet mode, producing only one progress message
    per 5 seconds. The default logging prints one message each 100,000
    rows, which often outputs many lines per second (especially on good
    hardware).

    This setting has no effect if `G` is specified in `-I`.

`-s` scale\_factor; `--scale=`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. When the scale is 20,000 or
    larger, the columns used to hold account identifiers (aid columns)
    will switch to using larger integers (`bigint`), in order to be big
    enough to hold the range of account identifiers.

`--foreign-keys`

:   Create foreign key constraints between the standard tables. (This
    option adds the `f` step to the initialization step sequence, if it
    is not already present.)

`--index-tablespace=index_tablespace`

:   Create indexes in the specified tablespace, rather than the default
    tablespace.

`--partition-method=NAME`

:   Create a partitioned `pgbench_accounts` table with NAME method.
    Expected values are `range` or `hash`. This option requires that
    `--partitions` is set to non-zero. If unspecified, default is
    `range`.

`--partitions=NUM`

:   Create a partitioned `pgbench_accounts` table with NUM partitions of
    nearly equal size for the scaled number of accounts. Default is `0`,
    meaning no partitioning.

`--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-run-options}
--------------------

pgbench accepts the following command-line benchmarking arguments:

`-b` scriptname\[@weight\]; `--builtin`=scriptname\[@weight\]

:   Add the specified built-in script to the list of scripts to be
    executed. Available built-in scripts are: `tpcb-like`,
    `simple-update` and `select-only`. Unambiguous prefixes of built-in
    names are accepted. With the special name `list`, show the list of
    built-in scripts and exit immediately.

    Optionally, write an integer weight after `@` to adjust the
    probability of selecting this script versus other ones. The default
    weight is 1. See below for details.

`-c` clients; `--client=`clients

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

`-C`; `--connect`

:   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`; `--debug`

:   Print debugging output.

`-D` varname`=`value; `--define=`varname`=`value

:   Define a variable for use by a custom script (see below). Multiple
    `-D` options are allowed.

`-f` filename\[@weight\]; `--file=`filename\[@weight\]

:   Add a transaction script read from filename to the list of scripts
    to be executed.

    Optionally, write an integer weight after `@` to adjust the
    probability of selecting this script versus other ones. The default
    weight is 1. (To use a script file name that includes an `@`
    character, append a weight so that there is no ambiguity, for
    example `filen@me@1`.) See below for details.

`-j` threads; `--jobs=`threads

:   Number of worker threads within pgbench. 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.

`-l`; `--log`

:   Write information about each transaction to a log file. See below
    for details.

`-L` limit; `--latency-limit=`limit

:   Transactions that last more than limit milliseconds are counted and
    reported separately, as late.

    When throttling is used (`--rate=...`), transactions that lag behind
    schedule by more than limit 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 skipped.

    When the `--max-tries` option is used, a transaction which fails due
    to a serialization anomaly or from a deadlock will not be retried if
    the total time of all its tries is greater than limit ms. To limit
    only the time of tries and not their number, use `--max-tries=0`. By
    default, the option `--max-tries` is set to 1 and transactions with
    serialization/deadlock errors are not retried. See [Failures and
    Serialization/Deadlock Retries](#failures-and-retries) for more
    information about retrying such transactions.

`-M` querymode; `--protocol=`querymode

:   Protocol to use for submitting queries to the server:

    -   `simple`: use simple query protocol.

    -   `extended`: use extended query protocol.

    -   `prepared`: use extended query protocol with prepared
        statements.

    In the `prepared` mode, pgbench reuses the parse analysis result
    starting from the second query iteration, so pgbench runs faster
    than in other modes.

    The default is simple query protocol. (See [???](#protocol) for more
    information.)

`-n`; `--no-vacuum`

:   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`; `--skip-some-updates`

:   Run built-in simple-update script. Shorthand for `-b simple-update`.

`-P` sec; `--progress=`sec

:   Show progress report every sec seconds. The report includes the time
    since the beginning of the run, the TPS since the last report, and
    the transaction latency average, standard deviation, and the number
    of failed transactions since the last report. Under throttling
    (`-R`), 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. When
    `--max-tries` is used to enable transaction retries after
    serialization/deadlock errors, the report includes the number of
    retried transactions and the sum of all retries.

`-r`; `--report-per-command`

:   Report the following statistics for each command after the benchmark
    finishes: the average per-statement latency (execution time from the
    perspective of the client), the number of failures and the number of
    retries after serialization or deadlock errors in this command. The
    report displays retry statistics only if the `--max-tries` option is
    not equal to 1.

`-R` rate; `--rate=`rate

:   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.

    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.

    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.

    If `--latency-limit` is used together with `--rate`, 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.

    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.

`-s` scale\_factor; `--scale=`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 only custom benchmarks (`-f` option),
    the scale factor will be reported as 1 unless this option is used.

`-S`; `--select-only`

:   Run built-in select-only script. Shorthand for `-b select-only`.

`-t` transactions; `--transactions=`transactions

:   Number of transactions each client runs. Default is 10.

`-T` seconds; `--time=`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`

:   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.

`--aggregate-interval=seconds`

:   Length of aggregation interval (in seconds). May be used only with
    `-l` option. With this option, the log contains per-interval summary
    data, as described below.

`--failures-detailed`

:   Report failures in per-transaction and aggregation logs, as well as
    in the main and per-script reports, grouped by the following types:

    -   serialization failures;

    -   deadlock failures;

    See [Failures and Serialization/Deadlock
    Retries](#failures-and-retries) for more information.

`--log-prefix=prefix`

:   Set the filename prefix for the log files created by `--log`. The
    default is `pgbench_log`.

`--max-tries=number_of_tries`

:   Enable retries for transactions with serialization/deadlock errors
    and set the maximum number of these tries. This option can be
    combined with the `--latency-limit` option which limits the total
    time of all transaction tries; moreover, you cannot use an unlimited
    number of tries (`--max-tries=0`) without `--latency-limit` or
    `--time`. The default value is 1 and transactions with
    serialization/deadlock errors are not retried. See [Failures and
    Serialization/Deadlock Retries](#failures-and-retries) for more
    information about retrying such transactions.

`--verbose-errors`

:   Print messages about all errors and failures (errors without
    retrying) including which limit for retries was exceeded and how far
    it was exceeded for the serialization/deadlock failures. (Note that
    in this case the output can be significantly increased.). See
    [Failures and Serialization/Deadlock Retries](#failures-and-retries)
    for more information.

`--progress-timestamp`

:   When showing progress (option `-P`), 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.

`--random-seed=`seed

:   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 seed may be: `time` (the default, the seed
    is based on the current time), `rand` (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
    (`random...` functions) or implicitly (for instance option `--rate`
    uses it to schedule transactions). When explicitly set, the value
    used for seeding is shown on the terminal. Any value allowed for
    seed may also be provided through the environment variable
    `PGBENCH_RANDOM_SEED`. To ensure that the provided seed impacts all
    possible uses, put this option first or use the environment
    variable.

    Setting the seed explicitly allows to reproduce a `pgbench` run
    exactly, as far as random numbers are concerned. As the random state
    is managed per thread, this means the exact same `pgbench` 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.

`--sampling-rate=rate`

:   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.

    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).

`--show-script=`scriptname

:   Show the actual code of builtin script scriptname on stderr, and
    exit immediately.

Common Options {#pgbench-common-options}
--------------

pgbench also accepts the following common command-line arguments for
connection parameters:

`-h` hostname; `--host=`hostname

:   The database server\'s host name

`-p` port; `--port=`port

:   The database server\'s port number

`-U` login; `--username=`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.

Exit Status
===========

A successful run will exit with status 0. Exit status 1 indicates static
problems such as invalid command-line options or internal errors which
are supposed to never occur. Early errors that occur when starting
benchmark such as initial connection failures also exit with status 1.
Errors during the run such as database errors or problems in the script
will result in exit status 2. In the latter case, pgbench will print
partial results.

Environment
===========

PGDATABASE; PGHOST; PGPORT; PGUSER

:   Default connection parameters.

This utility, like most other PostgreSQL utilities, uses the environment
variables supported by libpq (see [???](#libpq-envars)).

The environment variable PG\_COLOR specifies whether to use color in
diagnostic messages. Possible values are `always`, `auto` and `never`.

Notes
=====

What is the "Transaction" Actually Performed in pgbench? {#transactions-and-scripts}
--------------------------------------------------------

pgbench executes test scripts chosen randomly from a specified list. The
scripts may include built-in scripts specified with `-b` and
user-provided scripts specified with `-f`. Each script may be given a
relative weight specified after an `@` so as to change its selection
probability. The default weight is `1`. Scripts with a weight of `0` are
ignored.

The default built-in transaction script (also invoked with
`-b tpcb-like`) issues seven commands per transaction over randomly
chosen `aid`, `tid`, `bid` and `delta`. The scenario is inspired by the
TPC-B benchmark, but is not actually TPC-B, hence the name.

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 select the `simple-update` built-in (also `-N`), 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.

If you select the `select-only` built-in (also `-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.

A script file contains one or more SQL commands terminated by
semicolons. Empty lines and lines beginning with `--` are ignored.
Script files can also contain "meta commands", which are interpreted by
pgbench itself, as described below.

> **Note**
>
> Before PostgreSQL 9.6, SQL commands in script files were terminated by
> newlines, and so they could not be continued across lines. Now a
> semicolon is *required* to separate consecutive SQL commands (though
> an 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 pgbench, be sure to write each SQL command on a single
> line ending with a semicolon.
>
> It is assumed that pgbench scripts do not contain incomplete blocks of
> SQL transactions. If at runtime the client reaches the end of the
> script without completing the last transaction block, it will be
> aborted.

There is a simple variable-substitution facility for script files.
Variable names must consist of letters (including non-Latin letters),
digits, and underscores, with the first character not being a digit.
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, there are a few variables that are
preset automatically, listed in
[table\_title](#pgbench-automatic-variables). A value specified for
these variables using `-D` takes precedence over the automatic presets.
Once set, a variable\'s value can be inserted into an SQL command by
writing `:`variablename. When running more than one client session, each
session has its own set of variables. pgbench supports up to 255
variable uses in one statement.

  -------------------------------------------------------------------------
  Variable                 Description
  ------------------------ ------------------------------------------------
  `client_id`              unique number identifying the client session
                           (starts from zero)

  `default_seed`           seed used in hash and pseudorandom permutation
                           functions by default

  `random_seed`            random generator seed (unless overwritten with
                           `-D`)

  `scale`                  current scale factor
  -------------------------------------------------------------------------

  : pgbench Automatic Variables

Script file meta commands begin with a backslash (`\`) 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:

`\gset [prefix]` `\aset [prefix]`

:   These commands may be used to end SQL queries, taking the place of
    the terminating semicolon (`;`).

    When the `\gset` command is used, the preceding SQL query is
    expected to return one row, the columns of which are stored into
    variables named after column names, and prefixed with prefix if
    provided.

    When the `\aset` command is used, all combined SQL queries
    (separated by `\;`) have their columns stored into variables named
    after column names, and prefixed with prefix if provided. If a query
    returns no row, no assignment is made and the variable can be tested
    for existence to detect this. If a query returns more than one row,
    the last value is kept.

    `\gset` and `\aset` cannot be used in pipeline mode, since the query
    results are not yet available by the time the commands would need
    them.

    The following example puts the final account balance from the first
    query into variable abalance, and fills variables p\_two and
    p\_three with integers from the third query. The result of the
    second query is discarded. The result of the two last combined
    queries are stored in variables four and five.

        UPDATE pgbench_accounts
          SET abalance = abalance + :delta
          WHERE aid = :aid
          RETURNING abalance \gset
        -- compound of two queries
        SELECT 1 \;
        SELECT 2 AS two, 3 AS three \gset p_
        SELECT 4 AS four \; SELECT 5 AS five \aset

`\if` expression; `\elif` expression; `\else`; `\endif`

:   This group of commands implements nestable conditional blocks,
    similarly to `psql`\'s [???](#psql-metacommand-if). Conditional
    expressions are identical to those with `\set`, with non-zero values
    interpreted as true.

`\set varname expression`

:   Sets variable varname to a value calculated from expression. The
    expression may contain the `NULL` constant, Boolean constants `TRUE`
    and `FALSE`, integer constants such as `5432`, double constants such
    as `3.14159`, references to variables `:`variablename,
    [operators](#pgbench-builtin-operators) with their usual SQL
    precedence and associativity, [function
    calls](#pgbench-builtin-functions), SQL [CASE generic conditional
    expressions](#functions-case) and parentheses.

    Functions and most operators return `NULL` on `NULL` input.

    For conditional purposes, non zero numerical values are `TRUE`, zero
    numerical values and `NULL` are `FALSE`.

    Too large or small integer and double constants, as well as integer
    arithmetic operators (`+`, `-`, `*` and `/`) raise errors on
    overflows.

    When no final ELSE clause is provided to a CASE, the default value
    is `NULL`.

    Examples:

        \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

`\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
    with the given argument(s). The command must return an integer value
    through its standard output.

    command and each argument can be either a text constant or a
    `:`variablename reference to a variable. If you want to use an
    argument starting with a colon, write 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 of the command is discarded.

    Example:

        \shell command literal_argument :variable ::literal_starting_with_colon

`\startpipeline`; `\endpipeline`

:   These commands delimit the start and end of a pipeline of SQL
    statements. In pipeline mode, statements are sent to the server
    without waiting for the results of previous statements. See
    [???](#libpq-pipeline-mode) for more details. Pipeline mode requires
    the use of extended query protocol.

Built-in Operators {#pgbench-builtin-operators}
------------------

The arithmetic, bitwise, comparison and logical operators listed in
[table\_title](#pgbench-operators) are built into pgbench and may be
used in expressions appearing in [`\set`](#pgbench-metacommand-set). The
operators are listed in increasing precedence order. Except as noted,
operators taking two numeric inputs will produce a double value if
either input is double, otherwise they produce an integer result.

+--------------------------------------------------------------------------+
| Operator                                                                 |
|                                                                          |
| Description                                                              |
|                                                                          |
| Example(s)                                                               |
+==========================================================================+
| boolean `OR` boolean boolean                                             |
|                                                                          |
| Logical OR                                                               |
|                                                                          |
| `5 or 0` TRUE                                                            |
+--------------------------------------------------------------------------+
| boolean `AND` boolean boolean                                            |
|                                                                          |
| Logical AND                                                              |
|                                                                          |
| `3 and 0` FALSE                                                          |
+--------------------------------------------------------------------------+
| `NOT` boolean boolean                                                    |
|                                                                          |
| Logical NOT                                                              |
|                                                                          |
| `not false` TRUE                                                         |
+--------------------------------------------------------------------------+
| boolean `IS [NOT] (NULL|TRUE|FALSE)` boolean                             |
|                                                                          |
| Boolean value tests                                                      |
|                                                                          |
| `1 is null` FALSE                                                        |
+--------------------------------------------------------------------------+
| value `ISNULL|NOTNULL` boolean                                           |
|                                                                          |
| Nullness tests                                                           |
|                                                                          |
| `1 notnull` TRUE                                                         |
+--------------------------------------------------------------------------+
| number `=` number boolean                                                |
|                                                                          |
| Equal                                                                    |
|                                                                          |
| `5 = 4` FALSE                                                            |
+--------------------------------------------------------------------------+
| number `<>` number boolean                                               |
|                                                                          |
| Not equal                                                                |
|                                                                          |
| `5 <> 4` TRUE                                                            |
+--------------------------------------------------------------------------+
| number `!=` number boolean                                               |
|                                                                          |
| Not equal                                                                |
|                                                                          |
| `5 != 5` FALSE                                                           |
+--------------------------------------------------------------------------+
| number `<` number boolean                                                |
|                                                                          |
| Less than                                                                |
|                                                                          |
| `5 < 4` FALSE                                                            |
+--------------------------------------------------------------------------+
| number `<=` number boolean                                               |
|                                                                          |
| Less than or equal to                                                    |
|                                                                          |
| `5 <= 4` FALSE                                                           |
+--------------------------------------------------------------------------+
| number `>` number boolean                                                |
|                                                                          |
| Greater than                                                             |
|                                                                          |
| `5 > 4` TRUE                                                             |
+--------------------------------------------------------------------------+
| number `>=` number boolean                                               |
|                                                                          |
| Greater than or equal to                                                 |
|                                                                          |
| `5 >= 4` TRUE                                                            |
+--------------------------------------------------------------------------+
| integer `|` integer integer                                              |
|                                                                          |
| Bitwise OR                                                               |
|                                                                          |
| `1 | 2` 3                                                                |
+--------------------------------------------------------------------------+
| integer `#` integer integer                                              |
|                                                                          |
| Bitwise XOR                                                              |
|                                                                          |
| `1 # 3` 2                                                                |
+--------------------------------------------------------------------------+
| integer `&` integer integer                                              |
|                                                                          |
| Bitwise AND                                                              |
|                                                                          |
| `1 & 3` 1                                                                |
+--------------------------------------------------------------------------+
| `~` integer integer                                                      |
|                                                                          |
| Bitwise NOT                                                              |
|                                                                          |
| `~ 1` -2                                                                 |
+--------------------------------------------------------------------------+
| integer `<<` integer integer                                             |
|                                                                          |
| Bitwise shift left                                                       |
|                                                                          |
| `1 << 2` 4                                                               |
+--------------------------------------------------------------------------+
| integer `>>` integer integer                                             |
|                                                                          |
| Bitwise shift right                                                      |
|                                                                          |
| `8 >> 2` 2                                                               |
+--------------------------------------------------------------------------+
| number `+` number number                                                 |
|                                                                          |
| Addition                                                                 |
|                                                                          |
| `5 + 4` 9                                                                |
+--------------------------------------------------------------------------+
| number `-` number number                                                 |
|                                                                          |
| Subtraction                                                              |
|                                                                          |
| `3 - 2.0` 1.0                                                            |
+--------------------------------------------------------------------------+
| number `*` number number                                                 |
|                                                                          |
| Multiplication                                                           |
|                                                                          |
| `5 * 4` 20                                                               |
+--------------------------------------------------------------------------+
| number `/` number number                                                 |
|                                                                          |
| Division (truncates the result towards zero if both inputs are integers) |
|                                                                          |
| `5 / 3` 1                                                                |
+--------------------------------------------------------------------------+
| integer `%` integer integer                                              |
|                                                                          |
| Modulo (remainder)                                                       |
|                                                                          |
| `3 % 2` 1                                                                |
+--------------------------------------------------------------------------+
| `-` number number                                                        |
|                                                                          |
| Negation                                                                 |
|                                                                          |
| `- 2.0` -2.0                                                             |
+--------------------------------------------------------------------------+

: pgbench Operators

Built-In Functions {#pgbench-builtin-functions}
------------------

The functions listed in [table\_title](#pgbench-functions) are built
into pgbench and may be used in expressions appearing in
[`\set`](#pgbench-metacommand-set).

+-----------------------------------------------------------------------+
| Function                                                              |
|                                                                       |
| Description                                                           |
|                                                                       |
| Example(s)                                                            |
+=======================================================================+
| `abs` ( number ) same type as input                                   |
|                                                                       |
| Absolute value                                                        |
|                                                                       |
| `abs(-17)` 17                                                         |
+-----------------------------------------------------------------------+
| `debug` ( number ) same type as input                                 |
|                                                                       |
| Prints the argument to stderr, and returns the argument.              |
|                                                                       |
| `debug(5432.1)` 5432.1                                                |
+-----------------------------------------------------------------------+
| `double` ( number ) double                                            |
|                                                                       |
| Casts to double.                                                      |
|                                                                       |
| `double(5432)` 5432.0                                                 |
+-----------------------------------------------------------------------+
| `exp` ( number ) double                                               |
|                                                                       |
| Exponential (`e` raised to the given power)                           |
|                                                                       |
| `exp(1.0)` 2.718281828459045                                          |
+-----------------------------------------------------------------------+
| `greatest` ( number \[, `...`\] ) `double` if any argument is double, |
| else `integer`                                                        |
|                                                                       |
| Selects the largest value among the arguments.                        |
|                                                                       |
| `greatest(5, 4, 3, 2)` 5                                              |
+-----------------------------------------------------------------------+
| `hash` ( `value` \[, `seed`\] ) integer                               |
|                                                                       |
| This is an alias for `hash_murmur2`.                                  |
|                                                                       |
| `hash(10, 5432)` -5817877081768721676                                 |
+-----------------------------------------------------------------------+
| `hash_fnv1a` ( `value` \[, `seed`\] ) integer                         |
|                                                                       |
| Computes [FNV-1a                                                      |
| hash](https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_ha |
| sh_function).                                                         |
|                                                                       |
| `hash_fnv1a(10, 5432)` -7793829335365542153                           |
+-----------------------------------------------------------------------+
| `hash_murmur2` ( `value` \[, `seed`\] ) integer                       |
|                                                                       |
| Computes [MurmurHash2                                                 |
| hash](https://en.wikipedia.org/wiki/MurmurHash).                      |
|                                                                       |
| `hash_murmur2(10, 5432)` -5817877081768721676                         |
+-----------------------------------------------------------------------+
| `int` ( number ) integer                                              |
|                                                                       |
| Casts to integer.                                                     |
|                                                                       |
| `int(5.4 + 3.8)` 9                                                    |
+-----------------------------------------------------------------------+
| `least` ( number \[, `...`\] ) `double` if any argument is double,    |
| else `integer`                                                        |
|                                                                       |
| Selects the smallest value among the arguments.                       |
|                                                                       |
| `least(5, 4, 3, 2.1)` 2.1                                             |
+-----------------------------------------------------------------------+
| `ln` ( number ) double                                                |
|                                                                       |
| Natural logarithm                                                     |
|                                                                       |
| `ln(2.718281828459045)` 1.0                                           |
+-----------------------------------------------------------------------+
| `mod` ( integer, integer ) integer                                    |
|                                                                       |
| Modulo (remainder)                                                    |
|                                                                       |
| `mod(54, 32)` 22                                                      |
+-----------------------------------------------------------------------+
| `permute` ( `i`, `size` \[, `seed` \] ) integer                       |
|                                                                       |
| Permuted value of `i`, in the range `[0, size)`. This is the new      |
| position of `i` (modulo `size`) in a pseudorandom permutation of the  |
| integers `0...size-1`, parameterized by `seed`, see below.            |
|                                                                       |
| `permute(0, 4)` an integer between 0 and 3                            |
+-----------------------------------------------------------------------+
| `pi` () double                                                        |
|                                                                       |
| Approximate value of PI                                               |
|                                                                       |
| `pi()` 3.14159265358979323846                                         |
+-----------------------------------------------------------------------+
| `pow` ( `x`, `y` ) double                                             |
|                                                                       |
| `power` ( `x`, `y` ) double                                           |
|                                                                       |
| `x` raised to the power of `y`                                        |
|                                                                       |
| `pow(2.0, 10)` 1024.0                                                 |
+-----------------------------------------------------------------------+
| `random` ( `lb`, `ub` ) integer                                       |
|                                                                       |
| Computes a uniformly-distributed random integer in `[lb,              |
|         ub]`.                                                         |
|                                                                       |
| `random(1, 10)` an integer between 1 and 10                           |
+-----------------------------------------------------------------------+
| `random_exponential` ( `lb`, `ub`, `parameter` ) integer              |
|                                                                       |
| Computes an exponentially-distributed random integer in `[lb,         |
|         ub]`, see below.                                              |
|                                                                       |
| `random_exponential(1, 10, 3.0)` an integer between 1 and 10          |
+-----------------------------------------------------------------------+
| `random_gaussian` ( `lb`, `ub`, `parameter` ) integer                 |
|                                                                       |
| Computes a Gaussian-distributed random integer in `[lb,               |
|         ub]`, see below.                                              |
|                                                                       |
| `random_gaussian(1, 10, 2.5)` an integer between 1 and 10             |
+-----------------------------------------------------------------------+
| `random_zipfian` ( `lb`, `ub`, `parameter` ) integer                  |
|                                                                       |
| Computes a Zipfian-distributed random integer in `[lb,                |
|         ub]`, see below.                                              |
|                                                                       |
| `random_zipfian(1, 10, 1.5)` an integer between 1 and 10              |
+-----------------------------------------------------------------------+
| `sqrt` ( number ) double                                              |
|                                                                       |
| Square root                                                           |
|                                                                       |
| `sqrt(2.0)` 1.414213562                                               |
+-----------------------------------------------------------------------+

: pgbench Functions

The `random` function generates values using a uniform distribution,
that is all the values are drawn within the specified range with equal
probability. The `random_exponential`, `random_gaussian` and
`random_zipfian` functions require an additional double parameter which
determines the precise shape of the distribution.

-   For an exponential distribution, parameter controls the distribution
    by truncating a quickly-decreasing exponential distribution at
    parameter, and then projecting onto integers between the bounds. To
    be precise, with f(x) = exp(-parameter \* (x - min) / (max - min +
    1)) / (1 - exp(-parameter)) Then value i between min and max
    inclusive is drawn with probability: `f(i) - f(i + 1)`.

    Intuitively, the larger the parameter, the more frequently values
    close to min are accessed, and the less frequently values close to
    max are accessed. The closer to 0 parameter 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 min, are drawn parameter% of the time. The parameter value must
    be strictly positive.

-   For a Gaussian distribution, the interval is mapped onto a standard
    normal distribution (the classical bell-shaped Gaussian curve)
    truncated at `-parameter` on the left and `+parameter` on the right.
    Values in the middle of the interval are more likely to be drawn. To
    be precise, if `PHI(x)` is the cumulative distribution function of
    the standard normal distribution, with mean `mu` defined as
    `(max + min) / 2.0`, with f(x) = PHI(2.0 \* parameter \* (x - mu) /
    (max - min + 1)) / (2.0 \* PHI(parameter) - 1) then value i between
    min and max inclusive is drawn with probability:
    `f(i + 0.5) - f(i - 0.5)`. Intuitively, the larger the parameter,
    the more frequently values close to the middle of the interval are
    drawn, and the less frequently values close to the min and max
    bounds. About 67% of values are drawn from the middle
    `1.0 / parameter`, that is a relative `0.5 / parameter` around the
    mean, and 95% in the middle `2.0 / parameter`, that is a relative
    `1.0 / parameter` around the mean; for instance, if parameter is
    4.0, 67% of values are drawn from the middle quarter (1.0 / 4.0) of
    the interval (i.e., from `3.0 / 8.0` to `5.0 / 8.0`) and 95% from
    the middle half (`2.0 / 4.0`) of the interval (second and third
    quartiles). The minimum allowed parameter value is 2.0.

-   `random_zipfian` generates a bounded Zipfian distribution. parameter
    defines how skewed the distribution is. The larger the parameter,
    the more frequently values closer to the beginning of the interval
    are drawn. The distribution is such that, assuming the range starts
    from 1, the ratio of the probability of drawing k versus drawing k+1
    is `((k+1)/k)**parameter`. For example,
    `random_zipfian(1, ..., 2.5)` produces the value `1` about
    `(2/1)**2.5 =
          5.66` times more frequently than `2`, which itself is produced
    `(3/2)**2.5 = 2.76` times more frequently than `3`, and so on.

    pgbench\'s implementation is based on \"Non-Uniform Random Variate
    Generation\", Luc Devroye, p. 550-551, Springer 1986. Due to
    limitations of that algorithm, the parameter value is restricted to
    the range \[1.001, 1000\].

> **Note**
>
> When designing a benchmark which selects rows non-uniformly, be aware
> that the rows chosen may be correlated with other data such as IDs
> from a sequence or the physical row ordering, which may skew
> performance measurements.
>
> To avoid this, you may wish to use the `permute` function, or some
> other additional step with similar effect, to shuffle the selected
> rows and remove such correlations.

Hash functions `hash`, `hash_murmur2` and `hash_fnv1a` accept an input
value and an optional seed parameter. In case the seed isn\'t provided
the value of `:default_seed` is used, which is initialized randomly
unless set by the command-line `-D` option.

`permute` accepts an input value, a size, and an optional seed
parameter. It generates a pseudorandom permutation of integers in the
range `[0, size)`, and returns the index of the input value in the
permuted values. The permutation chosen is parameterized by the seed,
which defaults to `:default_seed`, if not specified. Unlike the hash
functions, `permute` ensures that there are no collisions or holes in
the output values. Input values outside the interval are interpreted
modulo the size. The function raises an error if the size is not
positive. `permute` can be used to scatter the distribution of
non-uniform random functions such as `random_zipfian` or
`random_exponential` so that values drawn more often are not trivially
correlated. For instance, the following pgbench script simulates a
possible real world workload typical for social media and blogging
platforms where a few accounts generate excessive load:

    \set size 1000000
    \set r random_zipfian(1, :size, 1.07)
    \set k 1 + permute(:r, :size)

In some cases several distinct distributions are needed which don\'t
correlate with each other and this is when the optional seed parameter
comes in handy:

    \set k1 1 + permute(:r, :size, :default_seed + 123)
    \set k2 1 + permute(:r, :size, :default_seed + 321)

A similar behavior can also be approximated with `hash`:

    \set size 1000000
    \set r random_zipfian(1, 100 * :size, 1.07)
    \set k 1 + abs(hash(:r)) % :size

However, since `hash` generates collisions, some values will not be
reachable and others will be more frequent than expected from the
original distribution.

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

    \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;

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 MDASH
otherwise they\'d not be independently touching different rows.)

Per-Transaction Logging
-----------------------

With the `-l` option (but without the `--aggregate-interval` option),
pgbench writes information about each transaction to a log file. The log
file will be named `prefix.nnn`, where prefix defaults to `pgbench_log`,
and nnn is the PID of the pgbench process. The prefix can be changed by
using the `--log-prefix` option. If the `-j` 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 `prefix.nnn.mmm`, where mmm is a sequential number
for each worker starting with 1.

Each line in a log file describes one transaction. It contains the
following space-separated fields:

client\_id

:   identifies the client session that ran the transaction

transaction\_no

:   counts how many transactions have been run by that session

time

:   transaction\'s elapsed time, in microseconds

script\_no

:   identifies the script file that was used for the transaction (useful
    when multiple scripts are specified with `-f` or `-b`)

time\_epoch

:   transaction\'s completion time, as a Unix-epoch time stamp

time\_us

:   fractional-second part of transaction\'s completion time, in
    microseconds

schedule\_lag

:   transaction start delay, that is the difference between the
    transaction\'s scheduled start time and the time it actually
    started, in microseconds (present only if `--rate` is specified)

retries

:   count of retries after serialization or deadlock errors during the
    transaction (present only if `--max-tries` is not equal to one)

When both `--rate` and `--latency-limit` are used, the time for a
skipped transaction will be reported as `skipped`. If the transaction
ends with a failure, its time will be reported as `failed`. If you use
the `--failures-detailed` option, the time of the failed transaction
will be reported as `serialization` or `deadlock` depending on the type
of failure (see [Failures and Serialization/Deadlock
Retries](#failures-and-retries) for more information).

Here is a snippet of a log file generated in a single-client run:

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

Another example with `--rate=100` and `--latency-limit=5` (note the
additional schedule\_lag column):

    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

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.

The following example shows a snippet of a log file with failures and
retries, with the maximum number of tries set to 10 (note the additional
retries column):

    3 0 47423 0 1499414498 34501 3
    3 1 8333 0 1499414498 42848 0
    3 2 8358 0 1499414498 51219 0
    4 0 72345 0 1499414498 59433 6
    1 3 41718 0 1499414498 67879 4
    1 4 8416 0 1499414498 76311 0
    3 3 33235 0 1499414498 84469 3
    0 0 failed 0 1499414498 84905 9
    2 0 failed 0 1499414498 86248 9
    3 4 8307 0 1499414498 92788 0

If the `--failures-detailed` option is used, the type of failure is
reported in the time like this:

    3 0 47423 0 1499414498 34501 3
    3 1 8333 0 1499414498 42848 0
    3 2 8358 0 1499414498 51219 0
    4 0 72345 0 1499414498 59433 6
    1 3 41718 0 1499414498 67879 4
    1 4 8416 0 1499414498 76311 0
    3 3 33235 0 1499414498 84469 3
    0 0 serialization 0 1499414498 84905 9
    2 0 serialization 0 1499414498 86248 9
    3 4 8307 0 1499414498 92788 0

When running a long test on hardware that can handle a lot of
transactions, the log files can become very large. The `--sampling-rate`
option can be used to log only a random sample of transactions.

Aggregated Logging
------------------

With the `--aggregate-interval` option, a different format is used for
the log files. Each log line describes one aggregation interval. It
contains the following space-separated fields:

interval\_start

:   start time of the interval, as a Unix-epoch time stamp

num\_transactions

:   number of transactions within the interval

sum\_latency

:   sum of transaction latencies

sum\_latency\_2

:   sum of squares of transaction latencies

min\_latency

:   minimum transaction latency

max\_latency

:   maximum transaction latency

sum\_lag

:   sum of transaction start delays (zero unless `--rate` is specified)

sum\_lag\_2

:   sum of squares of transaction start delays (zero unless `--rate` is
    specified)

min\_lag

:   minimum transaction start delay (zero unless `--rate` is specified)

max\_lag

:   maximum transaction start delay (zero unless `--rate` is specified)

skipped

:   number of transactions skipped because they would have started too
    late (zero unless `--rate` and `--latency-limit` are specified)

retried

:   number of retried transactions (zero unless `--max-tries` is not
    equal to one)

retries

:   number of retries after serialization or deadlock errors (zero
    unless `--max-tries` is not equal to one)

failures

:   number of transactions that ended with a failed SQL command

serialization\_failures

:   number of transactions that got a serialization error and were not
    retried afterwards (zero unless `--failures-detailed` is specified)

deadlock\_failures

:   number of transactions that got a deadlock error and were not
    retried afterwards (zero unless `--failures-detailed` is specified)

Here is some example output generated with these options:

    pgbench --aggregate-interval=10 --time=20 --client=10 --log --rate=1000 --latency-limit=10 --failures-detailed --max-tries=10 test

    1649114136 5815 27552565 177846919143 1078 21716 2756787 7264696105 0 9661 0 7854 31472 4022 4022 0
    1649114146 5958 28460110 182785513108 1083 20391 2539395 6411761497 0 7268 0 8127 32595 4101 4101 0

Notice that while the plain (unaggregated) log format shows which script
was used for each transaction, the aggregated format does not. Therefore
if you need per-script data, you need to aggregate the data on your own.

Per-Statement Report
--------------------

With the `-r` option, pgbench collects the following statistics for each
statement:

-   `latency` MDASH elapsed transaction time for each statement. pgbench
    reports an average value of all successful runs of the statement.

-   The number of failures in this statement. See [Failures and
    Serialization/Deadlock Retries](#failures-and-retries) for more
    information.

-   The number of retries after a serialization or a deadlock error in
    this statement. See [Failures and Serialization/Deadlock
    Retries](#failures-and-retries) for more information.

The report displays retry statistics only if the `--max-tries` option is
not equal to 1.

All values are computed for each statement executed by every client and
are reported after the benchmark has finished.

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

    starting vacuum...end.
    transaction type: <builtin: TPC-B (sort of)>
    scaling factor: 1
    query mode: simple
    number of clients: 10
    number of threads: 1
    maximum number of tries: 1
    number of transactions per client: 1000
    number of transactions actually processed: 10000/10000
    number of failed transactions: 0 (0.000%)
    number of transactions above the 50.0 ms latency limit: 1311/10000 (13.110 %)
    latency average = 28.488 ms
    latency stddev = 21.009 ms
    initial connection time = 69.068 ms
    tps = 346.224794 (without initial connection time)
    statement latencies in milliseconds and failures:
       0.012  0  \set aid random(1, 100000 * :scale)
       0.002  0  \set bid random(1, 1 * :scale)
       0.002  0  \set tid random(1, 10 * :scale)
       0.002  0  \set delta random(-5000, 5000)
       0.319  0  BEGIN;
       0.834  0  UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;
       0.641  0  SELECT abalance FROM pgbench_accounts WHERE aid = :aid;
      11.126  0  UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;
      12.961  0  UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;
       0.634  0  INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);
       1.957  0  END;

Another example of output for the default script using serializable
default transaction isolation level (`PGOPTIONS='-c
   default_transaction_isolation=serializable' pgbench ...`):

    starting vacuum...end.
    transaction type: <builtin: TPC-B (sort of)>
    scaling factor: 1
    query mode: simple
    number of clients: 10
    number of threads: 1
    maximum number of tries: 10
    number of transactions per client: 1000
    number of transactions actually processed: 6317/10000
    number of failed transactions: 3683 (36.830%)
    number of transactions retried: 7667 (76.670%)
    total number of retries: 45339
    number of transactions above the 50.0 ms latency limit: 106/6317 (1.678 %)
    latency average = 17.016 ms
    latency stddev = 13.283 ms
    initial connection time = 45.017 ms
    tps = 186.792667 (without initial connection time)
    statement latencies in milliseconds, failures and retries:
      0.006     0      0  \set aid random(1, 100000 * :scale)
      0.001     0      0  \set bid random(1, 1 * :scale)
      0.001     0      0  \set tid random(1, 10 * :scale)
      0.001     0      0  \set delta random(-5000, 5000)
      0.385     0      0  BEGIN;
      0.773     0      1  UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;
      0.624     0      0  SELECT abalance FROM pgbench_accounts WHERE aid = :aid;
      1.098   320   3762  UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;
      0.582  3363  41576  UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;
      0.465     0      0  INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);
      1.933     0      0  END;

If multiple script files are specified, all statistics 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.

Failures and Serialization/Deadlock Retries {#failures-and-retries}
-------------------------------------------

When executing pgbench, there are three main types of errors:

-   Errors of the main program. They are the most serious and always
    result in an immediate exit from pgbench with the corresponding
    error message. They include:

    -   errors at the beginning of pgbench (e.g. an invalid option
        value);

    -   errors in the initialization mode (e.g. the query to create
        tables for built-in scripts fails);

    -   errors before starting threads (e.g. could not connect to the
        database server, syntax error in the meta command, thread
        creation failure);

    -   internal pgbench errors (which are supposed to never occur\...).

-   Errors when the thread manages its clients (e.g. the client could
    not start a connection to the database server / the socket for
    connecting the client to the database server has become invalid). In
    such cases all clients of this thread stop while other threads
    continue to work.

-   Direct client errors. They lead to immediate exit from pgbench with
    the corresponding error message only in the case of an internal
    pgbench error (which are supposed to never occur\...). Otherwise in
    the worst case they only lead to the abortion of the failed client
    while other clients continue their run (but some client errors are
    handled without an abortion of the client and reported separately,
    see below). Later in this section it is assumed that the discussed
    errors are only the direct client errors and they are not internal
    pgbench errors.

A client\'s run is aborted in case of a serious error; for example, the
connection with the database server was lost or the end of script was
reached without completing the last transaction. In addition, if
execution of an SQL or meta command fails for reasons other than
serialization or deadlock errors, the client is aborted. Otherwise, if
an SQL command fails with serialization or deadlock errors, the client
is not aborted. In such cases, the current transaction is rolled back,
which also includes setting the client variables as they were before the
run of this transaction (it is assumed that one transaction script
contains only one transaction; see [What is the \"Transaction\" Actually
Performed in pgbench?](#transactions-and-scripts) for more information).
Transactions with serialization or deadlock errors are repeated after
rollbacks until they complete successfully or reach the maximum number
of tries (specified by the `--max-tries` option) / the maximum time of
retries (specified by the `--latency-limit` option) / the end of
benchmark (specified by the `--time` option). If the last trial run
fails, this transaction will be reported as failed but the client is not
aborted and continues to work.

> **Note**
>
> Without specifying the `--max-tries` option, a transaction will never
> be retried after a serialization or deadlock error because its default
> value is 1. Use an unlimited number of tries (`--max-tries=0`) and the
> `--latency-limit` option to limit only the maximum time of tries. You
> can also use the `--time` option to limit the benchmark duration under
> an unlimited number of tries.
>
> Be careful when repeating scripts that contain multiple transactions:
> the script is always retried completely, so successful transactions
> can be performed several times.
>
> Be careful when repeating transactions with shell commands. Unlike the
> results of SQL commands, the results of shell commands are not rolled
> back, except for the variable value of the `\setshell` command.

The latency of a successful transaction includes the entire time of
transaction execution with rollbacks and retries. The latency is
measured only for successful transactions and commands but not for
failed transactions or commands.

The main report contains the number of failed transactions. If the
`--max-tries` option is not equal to 1, the main report also contains
statistics related to retries: the total number of retried transactions
and total number of retries. The per-script report inherits all these
fields from the main report. The per-statement report displays retry
statistics only if the `--max-tries` option is not equal to 1.

If you want to group failures by basic types in per-transaction and
aggregation logs, as well as in the main and per-script reports, use the
`--failures-detailed` option. If you also want to distinguish all errors
and failures (errors without retrying) by type including which limit for
retries was exceeded and how much it was exceeded by for the
serialization/deadlock failures, use the `--verbose-errors` option.

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.

Security
--------

If untrusted users have access to a database that has not adopted a
[secure schema usage pattern](#ddl-schemas-patterns), do not run pgbench
in that database. pgbench uses unqualified names and does not manipulate
the search path.
