diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/ref/pgbench.sgml | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/doc/src/sgml/ref/pgbench.sgml b/doc/src/sgml/ref/pgbench.sgml index d52d324bf0d..41d90300981 100644 --- a/doc/src/sgml/ref/pgbench.sgml +++ b/doc/src/sgml/ref/pgbench.sgml @@ -680,6 +680,43 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d </varlistentry> <varlistentry> + <term><option>--random-seed=</option><replaceable>SEED</replaceable></term> + <listitem> + <para> + 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 <replaceable>SEED</replaceable> may be: + <literal>time</literal> (the default, the seed is based on the current time), + <literal>rand</literal> (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 + (<literal>random...</literal> functions) or implicitly (for instance option + <option>--rate</option> uses it to schedule transactions). + When explicitly set, the value used for seeding is shown on the terminal. + Any value allowed for <replaceable>SEED</replaceable> may also be + provided through the environment variable + <literal>PGBENCH_RANDOM_SEED</literal>. + To ensure that the provided seed impacts all possible uses, put this option + first or use the environment variable. + </para> + <para> + Setting the seed explicitly allows to reproduce a <command>pgbench</command> + run exactly, as far as random numbers are concerned. + As the random state is managed per thread, this means the exact same + <command>pgbench</command> 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. + </para> + </listitem> + </varlistentry> + + <varlistentry> <term><option>--sampling-rate=<replaceable>rate</replaceable></option></term> <listitem> <para> @@ -884,6 +921,11 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d </row> <row> + <entry> <literal>random_seed</literal> </entry> + <entry>random generator seed (unless overwritten with <option>-D</option>)</entry> + </row> + + <row> <entry> <literal>scale</literal> </entry> <entry>current scale factor</entry> </row> |