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Fix the usage of parallel and full options of vacuum command.

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Earlier we were inconsistent in allowing the usage of parallel and
full options.  Change it such that we disallow them only when they are
combined in a way that we don't support.

In passing, improve the comments in some of the existing tests of parallel
vacuum.

Reported-by: Tushar Ahuja
Author: Justin Pryzby, Amit Kapila
Reviewed-by: Sawada Masahiko, Michael Paquier, Mahendra Singh Thalor and
Amit Kapila
Discussion: https://postgr.es/m/58c8d171-e665-6fa3-a9d3-d9423b694dae%40enterprisedb.com
This commit is contained in:
Amit Kapila
2020-04-16 10:44:03 +05:30
parent 542d7817f7
commit 24d2d38b1e
4 changed files with 26 additions and 23 deletions
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32
doc/src/sgml/ref/vacuum.sgml
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@ -235,22 +235,22 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
Perform index vacuum and index cleanup phases of <command>VACUUM</command>
in parallel using <replaceable class="parameter">integer</replaceable>
background workers (for the details of each vacuum phase, please
refer to <xref linkend="vacuum-phases"/>). If the
<literal>PARALLEL</literal> option is omitted, then the number of workers
is determined based on the number of indexes that support parallel vacuum
operation on the relation, and is further limited by <xref
linkend="guc-max-parallel-workers-maintenance"/>.
An index can participate in parallel vacuum if and only if the size
of the index is more than <xref linkend="guc-min-parallel-index-scan-size"/>.
Please note that it is not guaranteed that the number of parallel workers
specified in <replaceable class="parameter">integer</replaceable> will
be used during execution. It is possible for a vacuum to run with fewer
workers than specified, or even with no workers at all. Only one worker
can be used per index. So parallel workers are launched only when there
are at least <literal>2</literal> indexes in the table. Workers for
vacuum are launched before the start of each phase and exit at the end of
the phase. These behaviors might change in a future release. This
option can't be used with the <literal>FULL</literal> option.
refer to <xref linkend="vacuum-phases"/>). In plain <command>VACUUM</command>
(without <literal>FULL</literal>), if the <literal>PARALLEL</literal> option
is omitted, then the number of workers is determined based on the number of
indexes on the relation that support parallel vacuum operation and is further
limited by <xref linkend="guc-max-parallel-workers-maintenance"/>. An index
can participate in parallel vacuum if and only if the size of the index is
more than <xref linkend="guc-min-parallel-index-scan-size"/>. Please note
that it is not guaranteed that the number of parallel workers specified in
<replaceable class="parameter">integer</replaceable> will be used during
execution. It is possible for a vacuum to run with fewer workers than
specified, or even with no workers at all. Only one worker can be used per
index. So parallel workers are launched only when there are at least
<literal>2</literal> indexes in the table. Workers for vacuum are launched
before the start of each phase and exit at the end of the phase. These
behaviors might change in a future release. This option can't be used with
the <literal>FULL</literal> option.
</para>
</listitem>
</varlistentry>