Allow UNIQUE indexes on partitioned tables

If we restrict unique constraints on partitioned tables so that they
must always include the partition key, then our standard approach to
unique indexes already works --- each unique key is forced to exist
within a single partition, so enforcing the unique restriction in each
index individually is enough to have it enforced globally.  Therefore we
can implement unique indexes on partitions by simply removing a few
restrictions (and adding others.)

Discussion: https://postgr.es/m/20171222212921.hi6hg6pem2w2t36z@alvherre.pgsql
Discussion: https://postgr.es/m/20171229230607.3iib6b62fn3uaf47@alvherre.pgsql
Reviewed-by: Simon Riggs, Jesper Pedersen, Peter Eisentraut, Jaime
	Casanova, Amit Langote

Author: alvherre

doc/src/sgml/ddl.sgml

@@ -3146,9 +3146,8 @@ CREATE TABLE measurement_y2006m02 PARTITION OF measurement
       <para>
        Create an index on the key column(s), as well as any other indexes you
        might want, on the partitioned table. (The key index is not strictly
-       necessary, but in most scenarios it is helpful.  If you intend the key
-       values to be unique then you should always create a unique or
-       primary-key constraint for each partition.)  This automatically creates
+       necessary, but in most scenarios it is helpful.)
+       This automatically creates
        one index on each partition, and any partitions you create or attach
        later will also contain the index.
 
@@ -3270,15 +3269,15 @@ ALTER TABLE measurement ATTACH PARTITION measurement_y2008m02
     <itemizedlist>
      <listitem>
       <para>
-       There is no way to create a primary key, unique constraint, or
+       There is no way to create a
        exclusion constraint spanning all partitions; it is only possible
        to constrain each leaf partition individually.
       </para>
      </listitem>
 
      <listitem>
       <para>
-       Since primary keys are not supported on partitioned tables, foreign
+       While primary keys are supported on partitioned tables, foreign
        keys referencing partitioned tables are not supported, nor are foreign
        key references from a partitioned table to some other table.
       </para>

doc/src/sgml/ref/alter_table.sgml

@@ -412,6 +412,11 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
       disappear too.
      </para>
 
+     <para>
+      Additional restrictions apply when unique or primary key constraints
+      are added to partitioned tables; see <xref linkend="sql-createtable" />.
+     </para>
+
      <note>
       <para>
        Adding a constraint using an existing index can be helpful in
@@ -834,9 +839,9 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
      <para>
       This form attaches an existing table (which might itself be partitioned)
       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>.  For each index in the target table, a corresponding
+      as a partition for specific values using <literal>FOR VALUES</literal>
+      or as a default partition by using <literal>DEFAULT</literal>.
+      For each index in the target table, a corresponding
       one will be created in the attached table; or, if an equivalent
       index already exists, will be attached to the target table's index,
       as if <command>ALTER INDEX ATTACH PARTITION</command> had been executed.
@@ -851,8 +856,10 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
       as the target table and no more; moreover, the column types must also
       match.  Also, it must have all the <literal>NOT NULL</literal> and
       <literal>CHECK</literal> constraints of the target table.  Currently
-      <literal>UNIQUE</literal>, <literal>PRIMARY KEY</literal>, and
       <literal>FOREIGN KEY</literal> constraints are not considered.
+      <literal>UNIQUE</literal> and <literal>PRIMARY KEY</literal> constraints
+      from the parent table will be created in the partition, if they don't
+      already exist.
       If any of the <literal>CHECK</literal> constraints of the table being
       attached is marked <literal>NO INHERIT</literal>, the command will fail;
       such a constraint must be recreated without the <literal>NO INHERIT</literal>

doc/src/sgml/ref/create_index.sgml

@@ -108,6 +108,11 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] <replaceable class=
         insert or update data which would result in duplicate entries
         will generate an error.
        </para>
+
+       <para>
+        Additional restrictions apply when unique indexes are applied to
+        partitioned tables; see <xref linkend="sql-createtable" />.
+       </para>
       </listitem>
      </varlistentry>
 

doc/src/sgml/ref/create_table.sgml

@@ -546,8 +546,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
      </para>
 
      <para>
-      Partitioned tables do not support <literal>UNIQUE</literal>,
-      <literal>PRIMARY KEY</literal>, <literal>EXCLUDE</literal>, or
+      Partitioned tables do not support <literal>EXCLUDE</literal> or
       <literal>FOREIGN KEY</literal> constraints; however, you can define
       these constraints on individual partitions.
      </para>
@@ -786,6 +785,14 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
       primary key constraint defined for the table.  (Otherwise it
       would just be the same constraint listed twice.)
      </para>
+
+     <para>
+      When used on partitioned tables, unique constraints must include all the
+      columns of the partition key.
+      If any partitions are in turn partitioned, all columns of each partition
+      key are considered at each level below the <literal>UNIQUE</literal>
+      constraint.
+     </para>
     </listitem>
    </varlistentry>
 
@@ -814,6 +821,13 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
       about the design of the schema, since a primary key implies that other
       tables can rely on this set of columns as a unique identifier for rows.
      </para>
+
+     <para>
+      <literal>PRIMARY KEY</literal> constraints share the restrictions that
+      <literal>UNIQUE</literal> constraints have when placed on partitioned
+      tables.
+     </para>
+
     </listitem>
    </varlistentry>
 

src/backend/bootstrap/bootparse.y

@@ -322,6 +322,7 @@ Boot_DeclareIndexStmt:
 								stmt,
 								$4,
 								InvalidOid,
+								InvalidOid,
 								false,
 								false,
 								false,
@@ -367,6 +368,7 @@ Boot_DeclareUniqueIndexStmt:
 								stmt,
 								$5,
 								InvalidOid,
+								InvalidOid,
 								false,
 								false,
 								false,

src/backend/catalog/index.c

@@ -691,6 +691,8 @@ UpdateIndexRelation(Oid indexoid,
  *		nonzero to specify a preselected OID.
  * parentIndexRelid: if creating an index partition, the OID of the
  *		parent index; otherwise InvalidOid.
+ * parentConstraintId: if creating a constraint on a partition, the OID
+ *		of the constraint in the parent; otherwise InvalidOid.
  * relFileNode: normally, pass InvalidOid to get new storage.  May be
  *		nonzero to attach an existing valid build.
  * indexInfo: same info executor uses to insert into the index
@@ -722,6 +724,7 @@ UpdateIndexRelation(Oid indexoid,
  *		(only if INDEX_CREATE_ADD_CONSTRAINT is set)
  * allow_system_table_mods: allow table to be a system catalog
  * is_internal: if true, post creation hook for new index
+ * constraintId: if not NULL, receives OID of created constraint
  *
  * Returns the OID of the created index.
  */
@@ -730,6 +733,7 @@ index_create(Relation heapRelation,
 			 const char *indexRelationName,
 			 Oid indexRelationId,
 			 Oid parentIndexRelid,
+			 Oid parentConstraintId,
 			 Oid relFileNode,
 			 IndexInfo *indexInfo,
 			 List *indexColNames,
@@ -742,7 +746,8 @@ index_create(Relation heapRelation,
 			 bits16 flags,
 			 bits16 constr_flags,
 			 bool allow_system_table_mods,
-			 bool is_internal)
+			 bool is_internal,
+			 Oid *constraintId)
 {
 	Oid			heapRelationId = RelationGetRelid(heapRelation);
 	Relation	pg_class;
@@ -989,6 +994,7 @@ index_create(Relation heapRelation,
 		if ((flags & INDEX_CREATE_ADD_CONSTRAINT) != 0)
 		{
 			char		constraintType;
+			ObjectAddress localaddr;
 
 			if (isprimary)
 				constraintType = CONSTRAINT_PRIMARY;
@@ -1002,14 +1008,17 @@ index_create(Relation heapRelation,
 				constraintType = 0; /* keep compiler quiet */
 			}
 
-			index_constraint_create(heapRelation,
+			localaddr = index_constraint_create(heapRelation,
 									indexRelationId,
+									parentConstraintId,
 									indexInfo,
 									indexRelationName,
 									constraintType,
 									constr_flags,
 									allow_system_table_mods,
 									is_internal);
+			if (constraintId)
+				*constraintId = localaddr.objectId;
 		}
 		else
 		{
@@ -1181,6 +1190,8 @@ index_create(Relation heapRelation,
  *
  * heapRelation: table owning the index (must be suitably locked by caller)
  * indexRelationId: OID of the index
+ * parentConstraintId: if constraint is on a partition, the OID of the
+ *		constraint in the parent.
  * indexInfo: same info executor uses to insert into the index
  * constraintName: what it say (generally, should match name of index)
  * constraintType: one of CONSTRAINT_PRIMARY, CONSTRAINT_UNIQUE, or
@@ -1198,6 +1209,7 @@ index_create(Relation heapRelation,
 ObjectAddress
 index_constraint_create(Relation heapRelation,
 						Oid indexRelationId,
+						Oid parentConstraintId,
 						IndexInfo *indexInfo,
 						const char *constraintName,
 						char constraintType,
@@ -1212,6 +1224,9 @@ index_constraint_create(Relation heapRelation,
 	bool		deferrable;
 	bool		initdeferred;
 	bool		mark_as_primary;
+	bool		islocal;
+	bool		noinherit;
+	int			inhcount;
 
 	deferrable = (constr_flags & INDEX_CONSTR_CREATE_DEFERRABLE) != 0;
 	initdeferred = (constr_flags & INDEX_CONSTR_CREATE_INIT_DEFERRED) != 0;
@@ -1246,6 +1261,19 @@ index_constraint_create(Relation heapRelation,
 		deleteDependencyRecordsForClass(RelationRelationId, indexRelationId,
 										RelationRelationId, DEPENDENCY_AUTO);
 
+	if (OidIsValid(parentConstraintId))
+	{
+		islocal = false;
+		inhcount = 1;
+		noinherit = false;
+	}
+	else
+	{
+		islocal = true;
+		inhcount = 0;
+		noinherit = true;
+	}
+
 	/*
 	 * Construct a pg_constraint entry.
 	 */
@@ -1273,9 +1301,9 @@ index_constraint_create(Relation heapRelation,
 								   NULL,	/* no check constraint */
 								   NULL,
 								   NULL,
-								   true,	/* islocal */
-								   0,	/* inhcount */
-								   true,	/* noinherit */
+								   islocal,
+								   inhcount,
+								   noinherit,
 								   is_internal);
 
 	/*
@@ -1294,6 +1322,18 @@ index_constraint_create(Relation heapRelation,
 
 	recordDependencyOn(&myself, &referenced, DEPENDENCY_INTERNAL);
 
+	/*
+	 * Also, if this is a constraint on a partition, mark it as depending
+	 * on the constraint in the parent.
+	 */
+	if (OidIsValid(parentConstraintId))
+	{
+		ObjectAddress	parentConstr;
+
+		ObjectAddressSet(parentConstr, ConstraintRelationId, parentConstraintId);
+		recordDependencyOn(&referenced, &parentConstr, DEPENDENCY_INTERNAL_AUTO);
+	}
+
 	/*
 	 * If the constraint is deferrable, create the deferred uniqueness
 	 * checking trigger.  (The trigger will be given an internal dependency on

src/backend/catalog/pg_constraint.c

@@ -747,6 +747,43 @@ AlterConstraintNamespaces(Oid ownerId, Oid oldNspId,
 	heap_close(conRel, RowExclusiveLock);
 }
 
+/*
+ * ConstraintSetParentConstraint
+ *		Set a partition's constraint as child of its parent table's
+ *
+ * This updates the constraint's pg_constraint row to show it as inherited, and
+ * add a dependency to the parent so that it cannot be removed on its own.
+ */
+void
+ConstraintSetParentConstraint(Oid childConstrId, Oid parentConstrId)
+{
+	Relation		constrRel;
+	Form_pg_constraint constrForm;
+	HeapTuple		tuple,
+					newtup;
+	ObjectAddress	depender;
+	ObjectAddress	referenced;
+
+	constrRel = heap_open(ConstraintRelationId, RowExclusiveLock);
+	tuple = SearchSysCache1(CONSTROID, ObjectIdGetDatum(childConstrId));
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for constraint %u", childConstrId);
+	newtup = heap_copytuple(tuple);
+	constrForm = (Form_pg_constraint) GETSTRUCT(newtup);
+	constrForm->conislocal = false;
+	constrForm->coninhcount++;
+	CatalogTupleUpdate(constrRel, &tuple->t_self, newtup);
+	ReleaseSysCache(tuple);
+
+	ObjectAddressSet(referenced, ConstraintRelationId, parentConstrId);
+	ObjectAddressSet(depender, ConstraintRelationId, childConstrId);
+
+	recordDependencyOn(&depender, &referenced, DEPENDENCY_INTERNAL_AUTO);
+
+	heap_close(constrRel, RowExclusiveLock);
+}
+
+
 /*
  * get_relation_constraint_oid
  *		Find a constraint on the specified relation with the specified name.
@@ -903,6 +940,45 @@ get_relation_constraint_attnos(Oid relid, const char *conname,
 	return conattnos;
 }
 
+/*
+ * Return the OID of the constraint associated with the given index in the
+ * given relation; or InvalidOid if no such index is catalogued.
+ */
+Oid
+get_relation_idx_constraint_oid(Oid relationId, Oid indexId)
+{
+	Relation	pg_constraint;
+	SysScanDesc	scan;
+	ScanKeyData	key;
+	HeapTuple	tuple;
+	Oid			constraintId = InvalidOid;
+
+	pg_constraint = heap_open(ConstraintRelationId, AccessShareLock);
+
+	ScanKeyInit(&key,
+				Anum_pg_constraint_conrelid,
+				BTEqualStrategyNumber,
+				F_OIDEQ,
+				ObjectIdGetDatum(relationId));
+	scan = systable_beginscan(pg_constraint, ConstraintRelidIndexId,
+							  true, NULL, 1, &key);
+	while ((tuple = systable_getnext(scan)) != NULL)
+	{
+		Form_pg_constraint	constrForm;
+
+		constrForm = (Form_pg_constraint) GETSTRUCT(tuple);
+		if (constrForm->conindid == indexId)
+		{
+			constraintId = HeapTupleGetOid(tuple);
+			break;
+		}
+	}
+	systable_endscan(scan);
+
+	heap_close(pg_constraint, AccessShareLock);
+	return constraintId;
+}
+
 /*
  * get_domain_constraint_oid
  *		Find a constraint on the specified domain with the specified name.

src/backend/catalog/toasting.c

@@ -330,13 +330,13 @@ create_toast_table(Relation rel, Oid toastOid, Oid toastIndexOid,
 	coloptions[1] = 0;
 
 	index_create(toast_rel, toast_idxname, toastIndexOid, InvalidOid,
-				 InvalidOid,
+				 InvalidOid, InvalidOid,
 				 indexInfo,
 				 list_make2("chunk_id", "chunk_seq"),
 				 BTREE_AM_OID,
 				 rel->rd_rel->reltablespace,
 				 collationObjectId, classObjectId, coloptions, (Datum) 0,
-				 INDEX_CREATE_IS_PRIMARY, 0, true, true);
+				 INDEX_CREATE_IS_PRIMARY, 0, true, true, NULL);
 
 	heap_close(toast_rel, NoLock);