diff options
Diffstat (limited to 'doc/src/sgml/ref/pgbench.sgml')
| -rw-r--r-- | doc/src/sgml/ref/pgbench.sgml | 59 |
1 files changed, 55 insertions, 4 deletions
diff --git a/doc/src/sgml/ref/pgbench.sgml b/doc/src/sgml/ref/pgbench.sgml index 5f280237991..f07ddf1226e 100644 --- a/doc/src/sgml/ref/pgbench.sgml +++ b/doc/src/sgml/ref/pgbench.sgml @@ -874,13 +874,18 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d <tbody> <row> - <entry> <literal>scale</literal> </entry> - <entry>current scale factor</entry> + <entry> <literal>client_id</literal> </entry> + <entry>unique number identifying the client session (starts from zero)</entry> </row> <row> - <entry> <literal>client_id</literal> </entry> - <entry>unique number identifying the client session (starts from zero)</entry> + <entry> <literal>default_seed</literal> </entry> + <entry>seed used in hash functions by default</entry> + </row> + + <row> + <entry> <literal>scale</literal> </entry> + <entry>current scale factor</entry> </row> </tbody> </tgroup> @@ -1246,6 +1251,27 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d <entry><literal>5</literal></entry> </row> <row> + <entry><literal><function>hash(<replaceable>a</replaceable> [, <replaceable>seed</replaceable> ] )</function></literal></entry> + <entry>integer</entry> + <entry>alias for <literal>hash_murmur2()</literal></entry> + <entry><literal>hash(10, 5432)</literal></entry> + <entry><literal>-5817877081768721676</literal></entry> + </row> + <row> + <entry><literal><function>hash_fnv1a(<replaceable>a</replaceable> [, <replaceable>seed</replaceable> ] )</function></literal></entry> + <entry>integer</entry> + <entry><ulink url="https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function">FNV-1a hash</ulink></entry> + <entry><literal>hash_fnv1a(10, 5432)</literal></entry> + <entry><literal>-7793829335365542153</literal></entry> + </row> + <row> + <entry><literal><function>hash_murmur2(<replaceable>a</replaceable> [, <replaceable>seed</replaceable> ] )</function></literal></entry> + <entry>integer</entry> + <entry><ulink url="https://en.wikipedia.org/wiki/MurmurHash">MurmurHash2 hash</ulink></entry> + <entry><literal>hash_murmur2(10, 5432)</literal></entry> + <entry><literal>-5817877081768721676</literal></entry> + </row> + <row> <entry><literal><function>int(<replaceable>x</replaceable>)</function></literal></entry> <entry>integer</entry> <entry>cast to int</entry> @@ -1424,6 +1450,31 @@ f(x) = PHI(2.0 * parameter * (x - mu) / (max - min + 1)) / </itemizedlist> <para> + Hash functions <literal>hash</literal>, <literal>hash_murmur2</literal> and + <literal>hash_fnv1a</literal> accept an input value and an optional seed parameter. + In case the seed isn't provided the value of <literal>:default_seed</literal> + is used, which is initialized randomly unless set by the command-line + <literal>-D</literal> option. Hash functions can be used to scatter the + distribution of random functions such as <literal>random_zipfian</literal> or + <literal>random_exponential</literal>. For instance, the following pgbench + script simulates possible real world workload typical for social media and + blogging platforms where few accounts generate excessive load: + +<programlisting> +\set r random_zipfian(0, 100000000, 1.07) +\set k abs(hash(:r)) % 1000000 +</programlisting> + + In some cases several distinct distributions are needed which don't correlate + with each other and this is when implicit seed parameter comes in handy: + +<programlisting> +\set k1 abs(hash(:r), :default_seed + 123) % 1000000 +\set k2 abs(hash(:r), :default_seed + 321) % 1000000 +</programlisting> + </para> + + <para> As an example, the full definition of the built-in TPC-B-like transaction is: |