1 files changed, 55 insertions, 6 deletions

diff --git a/doc/src/sgml/ref/vacuum.sgml b/doc/src/sgml/ref/vacuum.sgml
index f9b0fb87945..846056a353d 100644
--- a/doc/src/sgml/ref/vacuum.sgml
+++ b/doc/src/sgml/ref/vacuum.sgml
@@ -34,6 +34,7 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
     SKIP_LOCKED [ <replaceable class="parameter">boolean</replaceable> ]
     INDEX_CLEANUP [ <replaceable class="parameter">boolean</replaceable> ]
     TRUNCATE [ <replaceable class="parameter">boolean</replaceable> ]
+    PARALLEL <replaceable class="parameter">integer</replaceable>
 
 <phrase>and <replaceable class="parameter">table_and_columns</replaceable> is:</phrase>
 
@@ -75,10 +76,14 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
    with normal reading and writing of the table, as an exclusive lock
    is not obtained.  However, extra space is not returned to the operating
    system (in most cases); it's just kept available for re-use within the
-   same table.  <command>VACUUM FULL</command> rewrites the entire contents
-   of the table into a new disk file with no extra space, allowing unused
-   space to be returned to the operating system.  This form is much slower and
-   requires an exclusive lock on each table while it is being processed.
+   same table.  It also allows us to leverage multiple CPUs in order to process
+   indexes.  This feature is known as <firstterm>parallel vacuum</firstterm>.
+   To disable this feature, one can use <literal>PARALLEL</literal> option and
+   specify parallel workers as zero.  <command>VACUUM FULL</command> rewrites
+   the entire contents of the table into a new disk file with no extra space,
+   allowing unused space to be returned to the operating system.  This form is
+   much slower and requires an exclusive lock on each table while it is being
+   processed.
   </para>
 
   <para>
@@ -224,6 +229,33 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
    </varlistentry>
 
    <varlistentry>
+    <term><literal>PARALLEL</literal></term>
+    <listitem>
+     <para>
+      Perform vacuum index and cleanup index phases of <command>VACUUM</command>
+      in parallel using <replaceable class="parameter">integer</replaceable>
+      background workers (for the detail of each vacuum phases, please
+      refer to <xref linkend="vacuum-phases"/>).  If the
+      <literal>PARALLEL</literal> option is omitted, then
+      <command>VACUUM</command> decides the number of workers based on number
+      of indexes that support parallel vacuum operation on the relation which
+      is further limited by <xref linkend="guc-max-parallel-workers-maintenance"/>.
+      The index can participate in a 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 launches before starting 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>
+
+   <varlistentry>
     <term><replaceable class="parameter">boolean</replaceable></term>
     <listitem>
      <para>
@@ -238,6 +270,15 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
    </varlistentry>
 
    <varlistentry>
+    <term><replaceable class="parameter">integer</replaceable></term>
+    <listitem>
+     <para>
+      Specifies a non-negative integer value passed to the selected option.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
     <term><replaceable class="parameter">table_name</replaceable></term>
     <listitem>
      <para>
@@ -317,10 +358,18 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
    </para>
 
    <para>
+     The <option>PARALLEL</option> option is used only for vacuum purpose.
+     Even if this option is specified with <option>ANALYZE</option> option
+     it does not affect <option>ANALYZE</option>.
+   </para>
+
+   <para>
     <command>VACUUM</command> causes a substantial increase in I/O traffic,
     which might cause poor performance for other active sessions.  Therefore,
-    it is sometimes advisable to use the cost-based vacuum delay feature.
-    See <xref linkend="runtime-config-resource-vacuum-cost"/> for details.
+    it is sometimes advisable to use the cost-based vacuum delay feature.  For
+    parallel vacuum, each worker sleeps proportional to the work done by that
+    worker.  See <xref linkend="runtime-config-resource-vacuum-cost"/> for
+    details.
    </para>
 
    <para>