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Invent SERIALIZE option for EXPLAIN.

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EXPLAIN (ANALYZE, SERIALIZE) allows collection of statistics about
the volume of data emitted by a query, as well as the time taken
to convert the data to the on-the-wire format.  Previously there
was no way to investigate this without actually sending the data
to the client, in which case network transmission costs might
swamp what you wanted to see.  In particular this feature allows
investigating the costs of de-TOASTing compressed or out-of-line
data during formatting.

Stepan Rutz and Matthias van de Meent,
reviewed by Tomas Vondra and myself

Discussion: https://postgr.es/m/ca0adb0e-fa4e-c37e-1cd7-91170b18cae1@gmx.de
This commit is contained in:
Tom Lane
2024-04-03 17:41:54 -04:00
parent 97ce821e3e
commit 06286709ee
10 changed files with 542 additions and 11 deletions
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29
doc/src/sgml/ref/explain.sgml
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@@ -41,6 +41,7 @@ EXPLAIN [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] <rep
SETTINGS [ <replaceable class="parameter">boolean</replaceable> ]
GENERIC_PLAN [ <replaceable class="parameter">boolean</replaceable> ]
BUFFERS [ <replaceable class="parameter">boolean</replaceable> ]
SERIALIZE [ { NONE | TEXT | BINARY } ]
WAL [ <replaceable class="parameter">boolean</replaceable> ]
TIMING [ <replaceable class="parameter">boolean</replaceable> ]
SUMMARY [ <replaceable class="parameter">boolean</replaceable> ]
@@ -206,6 +207,34 @@ ROLLBACK;
</listitem>
</varlistentry>
<varlistentry>
<term><literal>SERIALIZE</literal></term>
<listitem>
<para>
Include information on the cost
of <firstterm>serializing</firstterm> the query's output data, that
is converting it to text or binary format to send to the client.
This can be a significant part of the time required for regular
execution of the query, if the datatype output functions are
expensive or if <acronym>TOAST</acronym>ed values must be fetched
from out-of-line storage. <command>EXPLAIN</command>'s default
behavior, <literal>SERIALIZE NONE</literal>, does not perform these
conversions. If <literal>SERIALIZE TEXT</literal>
or <literal>SERIALIZE BINARY</literal> is specified, the appropriate
conversions are performed, and the time spent doing so is measured
(unless <literal>TIMING OFF</literal> is specified). If
the <literal>BUFFERS</literal> option is also specified, then any
buffer accesses involved in the conversions are counted too.
In no case, however, will <command>EXPLAIN</command> actually send
the resulting data to the client; hence network transmission costs
cannot be investigated this way.
Serialization may only be enabled when <literal>ANALYZE</literal> is
also enabled. If <literal>SERIALIZE</literal> is written without an
argument, <literal>TEXT</literal> is assumed.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>WAL</literal></term>
<listitem>