Improvements to the partitioning documentation. Original patch from Greg

Stark, additional fixes and editorialization by Neil Conway. Greg's patch
description:

    Some more doc patches for partitioned tables. In particular replace
    the caveat that INCLUDING CONSTRAINTS doesn't exist and replace it
    with documentation of, well, INCLUDING CONSTRAINTS.

    Also, there was an instance of "LIKE WITH DEFAULTS" which is
    actually spelled "LIKE INCLUDING DEFAULTS".

Author: Neil Conway

doc/src/sgml/ddl.sgml

@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/ddl.sgml,v 1.61 2006/09/05 21:08:33 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/ddl.sgml,v 1.62 2006/09/20 01:20:38 neilc Exp $ -->
 
 <chapter id="ddl">
  <title>Data Definition</title>
@@ -2081,13 +2081,17 @@ VALUES ('New York', NULL, NULL, 'NY');
   </para>
 
   <para>
-   One convenient way to create a compatible table to be a new child is using
-   the <command>LIKE</command> option of <command>CREATE TABLE</command>. This
-   creates a table with the same columns with the same type (however note the
-   caveat below regarding constraints). Alternatively a compatible table can
+   One convenient way to create a compatible table to be a new child
+   is specify the <command>LIKE</command> clause in <command>CREATE
+   TABLE</command>. This creates a new table with the same columns as
+   the source table. If there are any <command>CHECK</command>
+   constraints defined on the parent table, the <command>INCLUDING
+   CONSTRAINTS</command> option to <command>LIKE</command> may be
+   useful, as the new child must have constraints matching the parent
+   to be considered compatible. Alternatively a compatible table can
    be created by first creating a new child using <command>CREATE
-   TABLE</command> then removing the inheritance link with <command>ALTER
-   TABLE</command>.
+   TABLE</command> then removing the inheritance link with
+   <command>ALTER TABLE</command>.
   </para>
 
   <para>
@@ -2159,19 +2163,6 @@ VALUES ('New York', NULL, NULL, 'NY');
      </para>
     </listitem>
 
-    <listitem>
-     <para>
-      There is no convenient way to define a table compatible with a specific
-      parent including columns and constraints. The <command>LIKE</command>
-      option for <command>CREATE TABLE</command> does not copy constraints
-      which makes the tables it creates ineligible for being added using
-      <command>ALTER TABLE</command>. Matching check constraints must be added 
-      manually or the table must be created as a child immediately, then if
-      needed removed from the inheritance structure temporarily to be added
-      again later.
-     </para>
-    </listitem>
-
     <listitem>
      <para>
       If a table is ever removed from the inheritance structure using
@@ -2577,56 +2568,86 @@ DO INSTEAD
         constraint for its partition.
        </para>
       </listitem>
+     </orderedlist>
+    </para>
 
-      <listitem>
-       <para>
-        When the time comes to archive and remove the old data we first remove
-        it from the production table using:
+    <para>
+     As we can see, a complex partitioning scheme could require a
+     substantial amount of DDL. In the above example we would be
+     creating a new partition each month, so it may be wise to write a
+     script that generates the required DDL automatically.
+    </para>
+
+   <sect2 id="ddl-partitioning-managing-partitions">
+   <title>Managing Partitions</title>
+
+   <para>
+     Normally the set of partitions established when initially
+     defining the table are not intended to remain static. It is
+     common to want to remove old partitions of data and periodically
+     add new partitions for new data. One of the most important
+     advantages of partitioning is precisely that it allows this
+     otherwise painful task to be executed nearly instantaneously by
+     manipulating the partition structure, rather than moving large
+     amounts of data around physically.
+   </para>
 
+   <para>
+     The simplest option for removing old data is to simply drop the partition
+     that is no longer necessary:
 <programlisting>
-ALTER TABLE measurement_y2003mm02 NO INHERIT measurement
+DROP TABLE measurement_y2003mm02;
 </programlisting>
+     This can very quickly delete millions of records because it doesn't have
+     to individually delete every record.
+   </para>
 
-        Then we can perform any sort of data modification necessary prior to
-        archiving without impacting the data viewed by the production system.
-        This could include, for example, deleting or compressing out redundant
-        data.
-       </para>
-      </listitem>
-      <listitem>
-      <para>
+   <para>
+     Another option that is often preferable is to remove the partition from
+     the partitioned table but retain access to it as a table in its own
+     right:
+<programlisting>
+ALTER TABLE measurement_y2003mm02 NO INHERIT measurement;
+</programlisting>
+     This allows further operations to be performed on the data before
+     it is dropped. For example, this is often a useful time to backup
+     the data using <command>COPY</>, <application>pg_dump</>, or
+     similar tools. It can also be a useful time to aggregate data
+     into smaller formats, perform other data manipulations, or run
+     reports.
+   </para>
 
-       Similarly we can a new partition to handle new data. We can either
-       create an empty partition as the original partitions were created
-       above, or for some applications it's necessary to bulk load and clean
-       data for the new partition. If that operation involves multiple steps
-       by different processes it can be helpful to work with it in a fresh
-       table outside of the master partitioned table until it's ready to be
-       loaded:
+   <para>
+     Similarly we can add a new partition to handle new data. We can create an
+     empty partition in the partitioned table just as the original partitions
+     were created above. 
 
 <programlisting>
-CREATE TABLE measurement_y2006m02 (LIKE measurement WITH DEFAULTS);
-\COPY measurement_y2006m02 FROM 'measurement_y2006m02'
-UPDATE ...
-ALTER TABLE measurement_y2006m02 ADD CONSTRAINT y2006m02 CHECK ( logdate &gt;= DATE '2006-02-01' AND logdate &lt DATE '2006-03-01' );
-ALTER TABLE measurement_y2006m02 INHERIT MEASUREMENT;
+CREATE TABLE measurement_y2006m02 (
+    CHECK ( logdate >= DATE '2006-02-01' AND logdate < DATE '2006-03-01' )
+) INHERITS (measurement);
 </programlisting>
 
-      </para>
-      </listitem>
-
-     </orderedlist>
-    </para>
+     As an alternative, it is sometimes more convenient to create the
+     new table outside the partition structure, and make it a proper
+     partition later. This allows the data to be loaded, checked, and
+     transformed prior to it appearing in the partitioned table.
 
-    <para>
-     As we can see, a complex partitioning scheme could require a
-     substantial amount of DDL. In the above example we would be
-     creating a new partition each month, so it may be wise to write a
-     script that generates the required DDL automatically.
+<programlisting>
+CREATE TABLE measurement_y2006m02 (LIKE measurement INCLUDING DEFAULTS INCLUDING CONSTRAINTS);
+\COPY measurement_y2006m02 FROM 'measurement_y2006m02'
+UPDATE ... ;
+ALTER TABLE measurement_y2006m02 ADD CONSTRAINT y2006m02 CHECK ( logdate >= DATE '2006-02-01' AND logdate < DATE '2006-03-01' );
+ALTER TABLE measurement_y2006m02 INHERIT measurement;
+</programlisting>
     </para>
+   </sect2>
 
+   <sect2 id="ddl-partitioning-caveats">
+   <title>Caveats</title>
+ 
    <para>
-    The following caveats apply:
+    The following caveats apply to partitioned tables:
    <itemizedlist>
     <listitem>
      <para>
@@ -2651,11 +2672,12 @@ ALTER TABLE measurement_y2006m02 INHERIT MEASUREMENT;
 
     <listitem>
      <para>
-      When using the <literal>LIKE</> option above to create new partitions
-      check constraints are not copied from the parent. If there are any check
-      constraints defined for the parent they must be manually created in new
-      partitions before <command>ALTER TABLE</command> will allow them to be
-      added.
+      When using the <literal>LIKE</> option above to create new
+      partitions, <literal>CHECK</> constraints are not copied from
+      the parent. If there are any <literal>CHECK</> constraints
+      defined for the parent, they must be manually created in new
+      partitions before <command>ALTER TABLE</command> will allow them
+      to be added.
      </para>
     </listitem>
    </itemizedlist>