database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-06-17 17:02:08 +03:00
Code Activity

Add general purpose hasing functions to pgbench.

Browse Source 
Hashing function is useful for simulating real-world workload in test like
WEB workload, as an example - YCSB benchmarks.

Author: Ildar Musin with minor editorization by me
Reviewed by: Fabien Coelho, me
Discussion: https://www.postgresql.org/message-id/flat/0e8bd39e-dfcd-2879-f88f-272799ad7ef2@postgrespro.ru
This commit is contained in:
Teodor Sigaev
2018-03-21 18:01:23 +03:00
parent 8bb3c7d347
commit e51a04840a
5 changed files with 237 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files

59
doc/src/sgml/ref/pgbench.sgml
View File

@ -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>
@ -1245,6 +1250,27 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d
<entry><literal>greatest(5, 4, 3, 2)</literal></entry>
<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>
@ -1423,6 +1449,31 @@ f(x) = PHI(2.0 * parameter * (x - mu) / (max - min + 1)) /
</listitem>
</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: