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pgbench: add \cset and \gset commands

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These commands allow assignment of values produced by queries to pgbench
variables, where they can be used by further commands.  \gset terminates
a command sequence (just like a bare semicolon); \cset separates
multiple queries in a compound command, like an escaped semicolon (\;).
A prefix can be provided to the \-command and is prepended to the name
of each output column to produce the final variable name.

This feature allows pgbench scripts to react meaningfully to the actual
database contents, allowing more powerful benchmarks to be written.

Authors: Fabien Coelho, Álvaro Herrera
Reviewed-by: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
Reviewed-by: Stephen Frost <sfrost@snowman.net>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Tatsuo Ishii <ishii@sraoss.co.jp>
Reviewed-by: Rafia Sabih <rafia.sabih@enterprisedb.com>
Discussion: https://postgr.es/m/alpine.DEB.2.20.1607091005330.3412@sto
This commit is contained in:
Alvaro Herrera
2019-01-10 13:42:20 -03:00
parent e1c1d5444e
commit 6260cc550b
6 changed files with 608 additions and 143 deletions
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85
doc/src/sgml/ref/pgbench.sgml
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@ -954,6 +954,91 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d
</para>
<variablelist>
<varlistentry id='pgbench-metacommand-cset'>
<term>
<literal>\cset [<replaceable>prefix</replaceable>]</literal>
</term>
<listitem>
<para>
This command may be used to end SQL queries, replacing an embedded
semicolon (<literal>\;</literal>) within a compound SQL command.
</para>
<para>
When this 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 <replaceable>prefix</replaceable> if provided.
</para>
<para>
The following example sends four queries as one compound SQL command,
inducing one message sent at the protocol level.
The result of the first query is stored into variable <replaceable>one</replaceable>,
the results of the third query are stored into variables <replaceable>z_three</replaceable>
and <replaceable>z_four</replaceable>,
whereas the results of the other queries are discarded.
<programlisting>
-- compound of four queries
SELECT 1 AS one \cset
SELECT 2 AS two \;
SELECT 3 AS three, 4 AS four \cset z_
SELECT 5;
</programlisting>
</para>
<note>
<para>
<literal>\cset</literal> does not work when empty SQL queries appear
within a compound SQL command.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry id='pgbench-metacommand-gset'>
<term>
<literal>\gset [<replaceable>prefix</replaceable>]</literal>
</term>
<listitem>
<para>
This command may be used to end SQL queries, replacing a final semicolon
(<literal>;</literal>).
</para>
<para>
When this 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 <replaceable>prefix</replaceable> if provided.
</para>
<para>
The following example puts the final account balance from the first query
into variable <replaceable>abalance</replaceable>, and fills variables
<replaceable>p_two</replaceable> and <replaceable>p_three</replaceable>
with integers from the last query.
The result of the second query is discarded.
<programlisting>
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_
</programlisting>
</para>
<note>
<para>
<literal>\gset</literal> does not work when empty SQL queries appear
within a compound SQL command.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>\if</literal> <replaceable class="parameter">expression</replaceable></term>
<term><literal>\elif</literal> <replaceable class="parameter">expression</replaceable></term>