Allow VACUUM to be run with index cleanup disabled.

This commit adds a new reloption, vacuum_index_cleanup, which
controls whether index cleanup is performed for a particular
relation by default.  It also adds a new option to the VACUUM
command, INDEX_CLEANUP, which can be used to override the
reloption.  If neither the reloption nor the VACUUM option is
used, the default is true, as before.

Masahiko Sawada, reviewed and tested by Nathan Bossart, Alvaro
Herrera, Kyotaro Horiguchi, Darafei Praliaskouski, and me.
The wording of the documentation is mostly due to me.

Discussion: http://postgr.es/m/CAD21AoAt5R3DNUZSjOoXDUY=naYPUOuffVsRzuTYMz29yLzQCA@mail.gmail.com

2 files changed, 38 insertions, 0 deletions

diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml
index 85c0ec1b318..1a8184e3063 100644
--- a/doc/src/sgml/ref/create_table.sgml
+++ b/doc/src/sgml/ref/create_table.sgml
@@ -1390,6 +1390,21 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
    </varlistentry>
 
    <varlistentry>
+    <term><literal>vacuum_index_cleanup</literal> (<type>boolean</type>)</term>
+    <listitem>
+     <para>
+      Enables or disables index cleanup when <command>VACUUM</command> is
+      run on this table.  The default value is <literal>true</literal>.
+      Disabling index cleanup can speed up <command>VACUUM</command> very
+      significantly, but may also lead to severely bloated indexes if table
+      modifications are frequent.  The <literal>INDEX_CLEANUP</literal>
+      parameter to <xref linkend="sql-vacuum"/>, if specified, overrides
+      the value of this option.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
     <term><literal>autovacuum_vacuum_threshold</literal>, <literal>toast.autovacuum_vacuum_threshold</literal> (<type>integer</type>)</term>
     <listitem>
      <para>
diff --git a/doc/src/sgml/ref/vacuum.sgml b/doc/src/sgml/ref/vacuum.sgml
index 906d0c2ad7c..fdd81512209 100644
--- a/doc/src/sgml/ref/vacuum.sgml
+++ b/doc/src/sgml/ref/vacuum.sgml
@@ -32,6 +32,7 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
     ANALYZE [ <replaceable class="parameter">boolean</replaceable> ]
     DISABLE_PAGE_SKIPPING [ <replaceable class="parameter">boolean</replaceable> ]
     SKIP_LOCKED [ <replaceable class="parameter">boolean</replaceable> ]
+    INDEX_CLEANUP [ <replaceable class="parameter">boolean</replaceable> ]
 
 <phrase>and <replaceable class="parameter">table_and_columns</replaceable> is:</phrase>
 
@@ -182,6 +183,28 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
    </varlistentry>
 
    <varlistentry>
+    <term><literal>INDEX_CLEANUP</literal></term>
+    <listitem>
+     <para>
+      Specifies that <command>VACUUM</command> should attempt to remove
+      index entries pointing to dead tuples.  This is normally the desired
+      behavior and is the default unless the
+      <literal>vacuum_index_cleanup</literal> option has been set to false
+      for the table to be vacuumed.  Setting this option to false may be
+      useful when it is necessary to make vacuum run as quickly as possible,
+      for example to avoid imminent transaction ID wraparound
+      (see <xref linkend="vacuum-for-wraparound"/>).  However, if index
+      cleanup is not performed regularly, performance may suffer, because
+      as the table is modified, indexes will accumulate dead tuples
+      and the table itself will accumulate dead line pointers that cannot be
+      removed until index cleanup is completed.  This option has no effect
+      for tables that do not have an index and is ignored if the
+      <literal>FULL</literal> is used.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
     <term><replaceable class="parameter">boolean</replaceable></term>
     <listitem>
      <para>