Add TABLESPACE option to REINDEX

This patch adds the possibility to move indexes to a new tablespace
while rebuilding them.  Both the concurrent and the non-concurrent cases
are supported, and the following set of restrictions apply:
- When using TABLESPACE with a REINDEX command that targets a
partitioned table or index, all the indexes of the leaf partitions are
moved to the new tablespace.  The tablespace references of the non-leaf,
partitioned tables in pg_class.reltablespace are not changed. This
requires an extra ALTER TABLE SET TABLESPACE.
- Any index on a toast table rebuilt as part of a parent table is kept
in its original tablespace.
- The operation is forbidden on system catalogs, including trying to
directly move a toast relation with REINDEX.  This results in an error
if doing REINDEX on a single object.  REINDEX SCHEMA, DATABASE and
SYSTEM skip system relations when TABLESPACE is used.

Author: Alexey Kondratov, Michael Paquier, Justin Pryzby
Reviewed-by: Álvaro Herrera, Michael Paquier
Discussion: https://postgr.es/m/8a8f5f73-00d3-55f8-7583-1375ca8f6a91@postgrespro.ru

doc/src/sgml/ref/reindex.sgml

@@ -26,6 +26,7 @@ REINDEX [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] { IN
 <phrase>where <replaceable class="parameter">option</replaceable> can be one of:</phrase>
 
     CONCURRENTLY [ <replaceable class="parameter">boolean</replaceable> ]
+    TABLESPACE <replaceable class="parameter">new_tablespace</replaceable>
     VERBOSE [ <replaceable class="parameter">boolean</replaceable> ]
 </synopsis>
  </refsynopsisdiv>
@@ -187,6 +188,15 @@ REINDEX [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] { IN
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>TABLESPACE</literal></term>
+    <listitem>
+     <para>
+      Specifies that indexes will be rebuilt on a new tablespace.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>VERBOSE</literal></term>
     <listitem>
@@ -210,6 +220,14 @@ REINDEX [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] { IN
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><replaceable class="parameter">new_tablespace</replaceable></term>
+    <listitem>
+     <para>
+      The tablespace where indexes will be rebuilt. 
+     </para>
+    </listitem>
+   </varlistentry>
   </variablelist>
  </refsect1>
 
@@ -294,7 +312,27 @@ REINDEX [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] { IN
    reindexed in a separate transaction. Those commands cannot be used inside
    a transaction block when working on a partitioned table or index.
   </para>
+  
+  <para>
+   When using the <literal>TABLESPACE</literal> clause with
+   <command>REINDEX</command> on a partitioned index or table, only the
+   tablespace references of the leaf partitions are updated. As partitioned
+   indexes are not updated, it is recommended to separately use
+   <command>ALTER TABLE ONLY</command> on them so as any new partitions
+   attached inherit the new tablespace. On failure, it may not have moved
+   all the indexes to the new tablespace. Re-running the command will rebuild
+   all the leaf partitions and move previously-unprocessed indexes to the new
+   tablespace.
+  </para>
 
+  <para>
+   If <literal>SCHEMA</literal>, <literal>DATABASE</literal> or
+   <literal>SYSTEM</literal> is used with <literal>TABLESPACE</literal>,
+   system relations are skipped and a single <literal>WARNING</literal>
+   will be generated. Indexes on TOAST tables are rebuilt, but not moved
+   to the new tablespace.
+  </para>
+   
   <refsect2 id="sql-reindex-concurrently" xreflabel="Rebuilding Indexes Concurrently">
    <title>Rebuilding Indexes Concurrently</title>