Initialization Options

pgbench accepts the following command-line initialization arguments:

Benchmarking Options

pgbench accepts the following command-line benchmarking arguments:

Common Options

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

What Is the “Transaction” Actually Performed in pgbench?

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.

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.

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 290. 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.

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:

Built-in Operators

The arithmetic, bitwise, comparison and logical operators listed in Table 291 are built into pgbench and may be used in expressions appearing in \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.

Built-In Functions

The functions listed in Table 292 are built into pgbench and may be used in expressions appearing in \set.

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.

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 — 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.

The format of the log is:

client_id transaction_no time script_no time_epoch time_us [ schedule_lag ] [ serialization_retries deadlock_retries ]

where client_id indicates which client session ran the transaction, transaction_no counts how many transactions have been run by that session, time is the total elapsed transaction time in microseconds, script_no identifies which script file was used (useful when multiple scripts were specified with -f or -b), and time_epoch/time_us are a Unix-epoch time stamp and an offset in microseconds (suitable for creating an ISO 8601 time stamp with fractional seconds) showing when the transaction completed. The schedule_lag field is the difference between the transaction's scheduled start time, and the time it actually started, in microseconds. It is only present when the --rate option is used. When both --rate and --latency-limit are used, the time for a skipped transaction will be reported as skipped. serialization_retries and deadlock_retries are the sums of all retries after the corresponding errors during the current script execution. They are only present when the maximum number of tries for transactions is not equal to 1 (--max-tries). If the transaction ended with a serialization/deadlock failure, its time will be reported as failed (see the section called “Serialization/Deadlock 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:

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

interval_start num_transactions​ sum_latency sum_latency_2 min_latency max_latency​ failed_tx [ sum_lag sum_lag_2 min_lag max_lag [ skipped ] ] [ retried_tx serialization_retries deadlock_retries ]

where interval_start is the start of the interval (as a Unix epoch time stamp), num_transactions is the number of transactions within the interval, sum_latency is the sum of the transaction latencies within the interval, sum_latency_2 is the sum of squares of the transaction latencies within the interval, min_latency is the minimum latency within the interval, max_latency is the maximum latency within the interval, and failed_tx is the number of transactions ended with serialization/deadlock failures within the interval (see the section called “Serialization/Deadlock Failures and Retries” for more information). The next fields, sum_lag, sum_lag_2, min_lag, and max_lag, are only present if the --rate option is used. They provide statistics about the time each transaction had to wait for the previous one to finish, i.e., the difference between each transaction's scheduled start time and the time it actually started. The next field, skipped, is only present if the --latency-limit option is used, too. It counts the number of transactions skipped because they would have started too late. The retried_tx, serialization_retries, and deadlock_retries fields are only present if the maximum number of tries for transactions is not equal to 1 (--max-tries). They report the number of retried transactions and the sum of all retries after the corresponding errors within the interval. Each transaction is counted in the interval when it was committed.

Here is some example output:

1345828501 5601 1542744 483552416 61 2573 0
1345828503 7884 1979812 565806736 60 1479 0
1345828505 7208 1979422 567277552 59 1391 0
1345828507 7685 1980268 569784714 60 1398 0
1345828509 7073 1979779 573489941 236 1411 0

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

Per-Statement Report

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

The report displays the columns with statistics on failures and retries only if the current pgbench run has a failure or retry of any type, respectively.

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)>
default transaction isolation level: read committed
transaction maximum tries number: 1
scaling factor: 1
query mode: simple
number of clients: 10
number of threads: 1
number of transactions per client: 1000
number of transactions actually processed: 10000/10000
latency average = 10.870 ms
latency stddev = 7.341 ms
initial connection time = 30.954 ms
tps = 907.949122 (without initial connection time)
statement latencies in milliseconds:
    0.001  \set aid random(1, 100000 * :scale)
    0.001  \set bid random(1, 1 * :scale)
    0.001  \set tid random(1, 10 * :scale)
    0.000  \set delta random(-5000, 5000)
    0.046  BEGIN;
    0.151  UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;
    0.107  SELECT abalance FROM pgbench_accounts WHERE aid = :aid;
    4.241  UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;
    5.245  UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;
    0.102  INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);
    0.974  END;

Another example of output for the default script using serializable default transaction isolation level (--default-isolation-level S):

starting vacuum...end.
transaction type: <builtin: TPC-B (sort of)>
default transaction isolation level: serializable
transaction maximum tries number: 100
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: 9676/10000
number of transactions failed: 324 (3.240 %)
number of transactions retried: 5629 (56.290 %)
number of retries: 103299 (serialization: 103299, deadlocks: 0)
number of transactions above the 100.0 ms latency limit: 21/9676 (0.217 %)
latency average = 16.138 ms
latency stddev = 21.017 ms
tps = 413.650224 (including connections establishing)
tps = 413.686560 (excluding connections establishing)
statement latencies in milliseconds, serialization failures and retries,
deadlock failures and retries:
  0.002    0      0  0  0  \set aid random(1, 100000 * :scale)
  0.000    0      0  0  0  \set bid random(1, 1 * :scale)
  0.000    0      0  0  0  \set tid random(1, 10 * :scale)
  0.000    0      0  0  0  \set delta random(-5000, 5000)
  0.121    0      0  0  0  BEGIN;
  0.290    0      2  0  0  UPDATE pgbench_accounts
                           SET abalance = abalance + :delta WHERE aid = :aid;
  0.221    0      0  0  0  SELECT abalance FROM pgbench_accounts
                           WHERE aid = :aid;
  0.266  212  72127  0  0  UPDATE pgbench_tellers
                           SET tbalance = tbalance + :delta WHERE tid = :tid;
  0.222  112  31170  0  0  UPDATE pgbench_branches
                           SET bbalance = bbalance + :delta WHERE bid = :bid;
  0.178    0      0  0  0  INSERT INTO pgbench_history
                                  (tid, bid, aid, delta, mtime)
                           VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);
  1.210    0      0  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.

Serialization/Deadlock Failures and Retries

Transactions with serialization or deadlock errors are rolled back and repeated until they complete successfully or reach the maximum number of tries specified by the --max-tries option. You can also limit the time of tries using the --latency-limit and/or --time options; in these cases, you can allow an unlimited number of tries within the specified time limits by setting the --max-tries option to zero. If the last transaction run fails, this transaction will be reported as failed. (It is assumed that one transaction script contains only one transaction; see the section called “What Is the “Transaction” Actually Performed in pgbench?” for more information.)

The latency of a successful transaction includes the entire time of transaction execution with rollbacks and retries. The latency for failed transactions and commands is not computed separately.

The main report contains the number of failed transactions if it is non-zero. If the total number of retried transactions is non-zero, the main report also contains the statistics related to retries: the total number of retried transactions, the total number of retries, and the number of retries after each kind of error. The per-statement report inherits all columns from the main report.

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, do not run pgbench in that database. pgbench uses unqualified names and does not manipulate the search path.