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Comments and doc fixes for commit 40d964ec99
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Reported-by: Justin Pryzby Author: Justin Pryzby, with few changes by me Reviewed-by: Amit Kapila and Sawada Masahiko Discussion: https://postgr.es/m/20200322021801.GB2563@telsasoft.com
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@ -232,15 +232,15 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
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<term><literal>PARALLEL</literal></term>
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<listitem>
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<para>
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Perform vacuum index and cleanup index phases of <command>VACUUM</command>
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Perform index vacuum and index cleanup phases of <command>VACUUM</command>
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in parallel using <replaceable class="parameter">integer</replaceable>
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background workers (for the detail of each vacuum phases, please
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background workers (for the details of each vacuum phase, please
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refer to <xref linkend="vacuum-phases"/>). If the
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<literal>PARALLEL</literal> option is omitted, then
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<command>VACUUM</command> decides the number of workers based on number
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of indexes that support parallel vacuum operation on the relation which
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is further limited by <xref linkend="guc-max-parallel-workers-maintenance"/>.
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The index can participate in a parallel vacuum if and only if the size
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<literal>PARALLEL</literal> option is omitted, then the number of workers
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is determined based on the number of indexes that support parallel vacuum
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operation on the relation, and is further limited by <xref
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linkend="guc-max-parallel-workers-maintenance"/>.
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An index can participate in parallel vacuum if and only if the size
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of the index is more than <xref linkend="guc-min-parallel-index-scan-size"/>.
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Please note that it is not guaranteed that the number of parallel workers
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specified in <replaceable class="parameter">integer</replaceable> will
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@ -248,7 +248,7 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
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workers than specified, or even with no workers at all. Only one worker
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can be used per index. So parallel workers are launched only when there
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are at least <literal>2</literal> indexes in the table. Workers for
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vacuum launches before starting each phase and exit at the end of
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vacuum are launched before the start of each phase and exit at the end of
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the phase. These behaviors might change in a future release. This
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option can't be used with the <literal>FULL</literal> option.
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</para>
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@ -358,8 +358,8 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
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</para>
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<para>
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The <option>PARALLEL</option> option is used only for vacuum purpose.
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Even if this option is specified with <option>ANALYZE</option> option
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The <option>PARALLEL</option> option is used only for vacuum purposes.
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If this option is specified with the <option>ANALYZE</option> option,
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it does not affect <option>ANALYZE</option>.
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</para>
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@ -367,7 +367,7 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
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<command>VACUUM</command> causes a substantial increase in I/O traffic,
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which might cause poor performance for other active sessions. Therefore,
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it is sometimes advisable to use the cost-based vacuum delay feature. For
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parallel vacuum, each worker sleeps proportional to the work done by that
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parallel vacuum, each worker sleeps in proportion to the work done by that
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worker. See <xref linkend="runtime-config-resource-vacuum-cost"/> for
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details.
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</para>
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