Allow a partitioned table to have a default partition.

Any tuples that don't route to any other partition will route to the
default partition.

Jeevan Ladhe, Beena Emerson, Ashutosh Bapat, Rahila Syed, and Robert
Haas, with review and testing at various stages by (at least) Rushabh
Lathia, Keith Fiske, Amit Langote, Amul Sul, Rajkumar Raghuanshi, Sven
Kunze, Kyotaro Horiguchi, Thom Brown, Rafia Sabih, and Dilip Kumar.

Discussion: http://postgr.es/m/CAH2L28tbN4SYyhS7YV1YBWcitkqbhSWfQCy0G=apRcC_PEO-bg@mail.gmail.com
Discussion: http://postgr.es/m/CAOG9ApEYj34fWMcvBMBQ-YtqR9fTdXhdN82QEKG0SVZ6zeL1xg@mail.gmail.com

Author: robertmhaas

doc/src/sgml/catalogs.sgml

@@ -4738,6 +4738,17 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</>:<replaceable>&lt;salt&gt;<
       <entry>The number of columns in partition key</entry>
      </row>
 
+     <row>
+      <entry><structfield>partdefid</structfield></entry>
+      <entry><type>oid</type></entry>
+      <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
+      <entry>
+       The OID of the <structname>pg_class</> entry for the default partition
+       of this partitioned table, or zero if this partitioned table does not
+       have a default partition.
+     </entry>
+     </row>
+
      <row>
       <entry><structfield>partattrs</structfield></entry>
       <entry><type>int2vector</type></entry>

doc/src/sgml/ref/alter_table.sgml

@@ -34,7 +34,7 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
 ALTER TABLE ALL IN TABLESPACE <replaceable class="PARAMETER">name</replaceable> [ OWNED BY <replaceable class="PARAMETER">role_name</replaceable> [, ... ] ]
     SET TABLESPACE <replaceable class="PARAMETER">new_tablespace</replaceable> [ NOWAIT ]
 ALTER TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
-    ATTACH PARTITION <replaceable class="PARAMETER">partition_name</replaceable> FOR VALUES <replaceable class="PARAMETER">partition_bound_spec</replaceable>
+    ATTACH PARTITION <replaceable class="PARAMETER">partition_name</replaceable> { FOR VALUES <replaceable class="PARAMETER">partition_bound_spec</replaceable> | DEFAULT }
 ALTER TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
     DETACH PARTITION <replaceable class="PARAMETER">partition_name</replaceable>
 
@@ -765,11 +765,18 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
    </varlistentry>
 
    <varlistentry>
-    <term><literal>ATTACH PARTITION <replaceable class="PARAMETER">partition_name</replaceable> FOR VALUES <replaceable class="PARAMETER">partition_bound_spec</replaceable></literal></term>
+    <term><literal>ATTACH PARTITION <replaceable class="PARAMETER">partition_name</replaceable> { FOR VALUES <replaceable class="PARAMETER">partition_bound_spec</replaceable> | DEFAULT }</literal></term>
     <listitem>
      <para>
       This form attaches an existing table (which might itself be partitioned)
-      as a partition of the target table using the same syntax for
+      as a partition of the target table. The table can be attached
+      as a partition for specific values using <literal>FOR VALUES
+      </literal> or as a default partition by using <literal>DEFAULT
+      </literal>.
+     </para>
+
+     <para>
+      A partition using <literal>FOR VALUES</literal> uses same syntax for
       <replaceable class="PARAMETER">partition_bound_spec</replaceable> as
       <xref linkend="sql-createtable">.  The partition bound specification
       must correspond to the partitioning strategy and partition key of the
@@ -806,6 +813,17 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
       (See the discussion in <xref linkend="SQL-CREATEFOREIGNTABLE"> about
       constraints on the foreign table.)
      </para>
+
+     <para>
+      When a table has a default partition, defining a new partition changes
+      the partition constraint for the default partition. The default
+      partition can't contain any rows that would need to be moved to the new
+      partition, and will be scanned to verify that none are present. This
+      scan, like the scan of the new partition, can be avoided if an
+      appropriate <literal>CHECK</literal> constraint is present. Also like
+      the scan of the new partition, it is always skipped when the default
+      partition is a foreign table.
+     </para>
     </listitem>
    </varlistentry>
 
@@ -1395,6 +1413,13 @@ ALTER TABLE cities
     ATTACH PARTITION cities_ab FOR VALUES IN ('a', 'b');
 </programlisting></para>
 
+  <para>
+   Attach a default partition to a partitioned table:
+<programlisting>
+ALTER TABLE cities
+    ATTACH PARTITION cities_partdef DEFAULT;
+</programlisting></para>
+
   <para>
    Detach a partition from partitioned table:
 <programlisting>

doc/src/sgml/ref/create_table.sgml

@@ -49,7 +49,7 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
   { <replaceable class="PARAMETER">column_name</replaceable> [ WITH OPTIONS ] [ <replaceable class="PARAMETER">column_constraint</replaceable> [ ... ] ]
     | <replaceable>table_constraint</replaceable> }
     [, ... ]
-) ] FOR VALUES <replaceable class="PARAMETER">partition_bound_spec</replaceable>
+) ] { FOR VALUES <replaceable class="PARAMETER">partition_bound_spec</replaceable> | DEFAULT }
 [ PARTITION BY { RANGE | LIST } ( { <replaceable class="parameter">column_name</replaceable> | ( <replaceable class="parameter">expression</replaceable> ) } [ COLLATE <replaceable class="parameter">collation</replaceable> ] [ <replaceable class="parameter">opclass</replaceable> ] [, ... ] ) ]
 [ WITH ( <replaceable class="PARAMETER">storage_parameter</replaceable> [= <replaceable class="PARAMETER">value</replaceable>] [, ... ] ) | WITH OIDS | WITHOUT OIDS ]
 [ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
@@ -250,11 +250,13 @@ FROM ( { <replaceable class="PARAMETER">numeric_literal</replaceable> | <replace
    </varlistentry>
 
    <varlistentry id="SQL-CREATETABLE-PARTITION">
-    <term><literal>PARTITION OF <replaceable class="PARAMETER">parent_table</replaceable> FOR VALUES <replaceable class="PARAMETER">partition_bound_spec</replaceable></literal></term>
+    <term><literal>PARTITION OF <replaceable class="PARAMETER">parent_table</replaceable> { FOR VALUES <replaceable class="PARAMETER">partition_bound_spec</replaceable> | DEFAULT }</literal></term>
     <listitem>
      <para>
       Creates the table as a <firstterm>partition</firstterm> of the specified
-      parent table.
+      parent table. The table can be created either as a partition for specific
+      values using <literal>FOR VALUES</literal> or as a default partition
+      using <literal>DEFAULT</literal>.
      </para>
 
      <para>
@@ -342,6 +344,26 @@ FROM ( { <replaceable class="PARAMETER">numeric_literal</replaceable> | <replace
       allows precisely one value to be stored &mdash; "infinity".
      </para>
 
+     <para>
+      If <literal>DEFAULT</literal> is specified, the table will be
+      created as a default partition of the parent table. The parent can
+      either be a list or range partitioned table. A partition key value
+      not fitting into any other partition of the given parent will be
+      routed to the default partition. There can be only one default
+      partition for a given parent table.
+     </para>
+
+     <para>
+      When a table has an existing <literal>DEFAULT</literal> partition and
+      a new partition is added to it, the existing default partition must
+      be scanned to verify that it does not contain any rows which properly
+      belong in the new partition.  If the default partition contains a
+      large number of rows, this may be slow.  The scan will be skipped if
+      the default partition is a foreign table or if it has a constraint which
+      proves that it cannot contain rows which should be placed in the new
+      partition.
+     </para>
+
      <para>
       A partition must have the same column names and types as the partitioned
       table to which it belongs.  If the parent is specified <literal>WITH
@@ -1679,6 +1701,13 @@ CREATE TABLE cities_ab
 CREATE TABLE cities_ab_10000_to_100000
     PARTITION OF cities_ab FOR VALUES FROM (10000) TO (100000);
 </programlisting></para>
+
+  <para>
+   Create a default partition:
+<programlisting>
+CREATE TABLE cities_partdef
+    PARTITION OF cities DEFAULT;
+</programlisting></para>
  </refsect1>
 
  <refsect1 id="SQL-CREATETABLE-compatibility">

src/backend/catalog/heap.c

@@ -1759,7 +1759,8 @@ heap_drop_with_catalog(Oid relid)
 {
 	Relation	rel;
 	HeapTuple	tuple;
-	Oid			parentOid = InvalidOid;
+	Oid			parentOid = InvalidOid,
+				defaultPartOid = InvalidOid;
 
 	/*
 	 * To drop a partition safely, we must grab exclusive lock on its parent,
@@ -1775,6 +1776,14 @@ heap_drop_with_catalog(Oid relid)
 	{
 		parentOid = get_partition_parent(relid);
 		LockRelationOid(parentOid, AccessExclusiveLock);
+
+		/*
+		 * If this is not the default partition, dropping it will change the
+		 * default partition's partition constraint, so we must lock it.
+		 */
+		defaultPartOid = get_default_partition_oid(parentOid);
+		if (OidIsValid(defaultPartOid) && relid != defaultPartOid)
+			LockRelationOid(defaultPartOid, AccessExclusiveLock);
 	}
 
 	ReleaseSysCache(tuple);
@@ -1825,6 +1834,13 @@ heap_drop_with_catalog(Oid relid)
 	if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
 		RemovePartitionKeyByRelId(relid);
 
+	/*
+	 * If the relation being dropped is the default partition itself,
+	 * invalidate its entry in pg_partitioned_table.
+	 */
+	if (relid == defaultPartOid)
+		update_default_partition_oid(parentOid, InvalidOid);
+
 	/*
 	 * Schedule unlinking of the relation's physical files at commit.
 	 */
@@ -1884,6 +1900,14 @@ heap_drop_with_catalog(Oid relid)
 
 	if (OidIsValid(parentOid))
 	{
+		/*
+		 * If this is not the default partition, the partition constraint of
+		 * the default partition has changed to include the portion of the key
+		 * space previously covered by the dropped partition.
+		 */
+		if (OidIsValid(defaultPartOid) && relid != defaultPartOid)
+			CacheInvalidateRelcacheByRelid(defaultPartOid);
+
 		/*
 		 * Invalidate the parent's relcache so that the partition is no longer
 		 * included in its partition descriptor.
@@ -3138,6 +3162,7 @@ StorePartitionKey(Relation rel,
 	values[Anum_pg_partitioned_table_partrelid - 1] = ObjectIdGetDatum(RelationGetRelid(rel));
 	values[Anum_pg_partitioned_table_partstrat - 1] = CharGetDatum(strategy);
 	values[Anum_pg_partitioned_table_partnatts - 1] = Int16GetDatum(partnatts);
+	values[Anum_pg_partitioned_table_partdefid - 1] = ObjectIdGetDatum(InvalidOid);
 	values[Anum_pg_partitioned_table_partattrs - 1] = PointerGetDatum(partattrs_vec);
 	values[Anum_pg_partitioned_table_partclass - 1] = PointerGetDatum(partopclass_vec);
 	values[Anum_pg_partitioned_table_partcollation - 1] = PointerGetDatum(partcollation_vec);
@@ -3223,7 +3248,8 @@ RemovePartitionKeyByRelId(Oid relid)
  *		relispartition to true
  *
  * Also, invalidate the parent's relcache, so that the next rebuild will load
- * the new partition's info into its partition descriptor.
+ * the new partition's info into its partition descriptor.  If there is a
+ * default partition, we must invalidate its relcache entry as well.
  */
 void
 StorePartitionBound(Relation rel, Relation parent, PartitionBoundSpec *bound)
@@ -3234,6 +3260,7 @@ StorePartitionBound(Relation rel, Relation parent, PartitionBoundSpec *bound)
 	Datum		new_val[Natts_pg_class];
 	bool		new_null[Natts_pg_class],
 				new_repl[Natts_pg_class];
+	Oid			defaultPartOid;
 
 	/* Update pg_class tuple */
 	classRel = heap_open(RelationRelationId, RowExclusiveLock);
@@ -3271,5 +3298,15 @@ StorePartitionBound(Relation rel, Relation parent, PartitionBoundSpec *bound)
 	heap_freetuple(newtuple);
 	heap_close(classRel, RowExclusiveLock);
 
+	/*
+	 * The partition constraint for the default partition depends on the
+	 * partition bounds of every other partition, so we must invalidate the
+	 * relcache entry for that partition every time a partition is added or
+	 * removed.
+	 */
+	defaultPartOid = get_default_oid_from_partdesc(RelationGetPartitionDesc(parent));
+	if (OidIsValid(defaultPartOid))
+		CacheInvalidateRelcacheByRelid(defaultPartOid);
+
 	CacheInvalidateRelcache(parent);
 }