Allow some exclusion constraints on partitions

Previously we only allowed unique B-tree constraints on partitions
(and only if the constraint included all the partition keys).  But we
could allow exclusion constraints with the same restriction.  We also
require that those columns be compared for equality, not something
like &&.

Author: Paul A. Jungwirth <pj@illuminatedcomputing.com>
Reviewed-by: Ronan Dunklau <ronan.dunklau@aiven.io>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://www.postgresql.org/message-id/flat/ec8b1d9b-502e-d1f8-e909-1bf9dffe6fa5@illuminatedcomputing.com

contrib/btree_gist/Makefile

@@ -38,7 +38,7 @@ PGFILEDESC = "btree_gist - B-tree equivalent GiST operator classes"
 
 REGRESS = init int2 int4 int8 float4 float8 cash oid timestamp timestamptz \
         time timetz date interval macaddr macaddr8 inet cidr text varchar char \
-        bytea bit varbit numeric uuid not_equal enum bool
+        bytea bit varbit numeric uuid not_equal enum bool partitions
 
 SHLIB_LINK += $(filter -lm, $(LIBS))
 

contrib/btree_gist/expected/partitions.out

@@ -0,0 +1,82 @@
+-- Make sure we can create an exclusion constraint
+-- across a partitioned table.
+-- That code looks at strategy numbers that can differ in regular gist vs btree_gist,
+-- so we want to make sure it works here too.
+create table parttmp (
+  id int,
+  valid_at daterange,
+  exclude using gist (id with =, valid_at with &&)
+) partition by range (id);
+create table parttmp_1_to_10 partition of parttmp for values from (1) to (10);
+create table parttmp_11_to_20 partition of parttmp for values from (11) to (20);
+insert into parttmp (id, valid_at) values
+  (1, '[2000-01-01, 2000-02-01)'),
+  (1, '[2000-02-01, 2000-03-01)'),
+  (2, '[2000-01-01, 2000-02-01)'),
+  (11, '[2000-01-01, 2000-02-01)'),
+  (11, '[2000-02-01, 2000-03-01)'),
+  (12, '[2000-01-01, 2000-02-01)');
+select * from parttmp order by id, valid_at;
+ id |        valid_at         
+----+-------------------------
+  1 | [01-01-2000,02-01-2000)
+  1 | [02-01-2000,03-01-2000)
+  2 | [01-01-2000,02-01-2000)
+ 11 | [01-01-2000,02-01-2000)
+ 11 | [02-01-2000,03-01-2000)
+ 12 | [01-01-2000,02-01-2000)
+(6 rows)
+
+select * from parttmp_1_to_10 order by id, valid_at;
+ id |        valid_at         
+----+-------------------------
+  1 | [01-01-2000,02-01-2000)
+  1 | [02-01-2000,03-01-2000)
+  2 | [01-01-2000,02-01-2000)
+(3 rows)
+
+select * from parttmp_11_to_20 order by id, valid_at;
+ id |        valid_at         
+----+-------------------------
+ 11 | [01-01-2000,02-01-2000)
+ 11 | [02-01-2000,03-01-2000)
+ 12 | [01-01-2000,02-01-2000)
+(3 rows)
+
+update parttmp set valid_at = valid_at * '[2000-01-15,2000-02-15)' where id = 1;
+select * from parttmp order by id, valid_at;
+ id |        valid_at         
+----+-------------------------
+  1 | [01-15-2000,02-01-2000)
+  1 | [02-01-2000,02-15-2000)
+  2 | [01-01-2000,02-01-2000)
+ 11 | [01-01-2000,02-01-2000)
+ 11 | [02-01-2000,03-01-2000)
+ 12 | [01-01-2000,02-01-2000)
+(6 rows)
+
+select * from parttmp_1_to_10 order by id, valid_at;
+ id |        valid_at         
+----+-------------------------
+  1 | [01-15-2000,02-01-2000)
+  1 | [02-01-2000,02-15-2000)
+  2 | [01-01-2000,02-01-2000)
+(3 rows)
+
+select * from parttmp_11_to_20 order by id, valid_at;
+ id |        valid_at         
+----+-------------------------
+ 11 | [01-01-2000,02-01-2000)
+ 11 | [02-01-2000,03-01-2000)
+ 12 | [01-01-2000,02-01-2000)
+(3 rows)
+
+-- make sure the excluson constraint excludes:
+insert into parttmp (id, valid_at) values
+  (2, '[2000-01-15, 2000-02-01)');
+ERROR:  conflicting key value violates exclusion constraint "parttmp_1_to_10_id_valid_at_excl"
+DETAIL:  Key (id, valid_at)=(2, [01-15-2000,02-01-2000)) conflicts with existing key (id, valid_at)=(2, [01-01-2000,02-01-2000)).
+drop table parttmp;
+-- should fail with a good error message:
+create table parttmp (id int, valid_at daterange, exclude using gist (id with <>, valid_at with &&)) partition by range (id);
+ERROR:  cannot match partition key to index on column "id" using non-equal operator "<>"

contrib/btree_gist/meson.build

@@ -88,6 +88,7 @@ tests += {
       'not_equal',
       'enum',
       'bool',
+      'partitions',
     ],
   },
 }

contrib/btree_gist/sql/partitions.sql

@@ -0,0 +1,39 @@
+-- Make sure we can create an exclusion constraint
+-- across a partitioned table.
+-- That code looks at strategy numbers that can differ in regular gist vs btree_gist,
+-- so we want to make sure it works here too.
+create table parttmp (
+  id int,
+  valid_at daterange,
+  exclude using gist (id with =, valid_at with &&)
+) partition by range (id);
+
+create table parttmp_1_to_10 partition of parttmp for values from (1) to (10);
+create table parttmp_11_to_20 partition of parttmp for values from (11) to (20);
+
+insert into parttmp (id, valid_at) values
+  (1, '[2000-01-01, 2000-02-01)'),
+  (1, '[2000-02-01, 2000-03-01)'),
+  (2, '[2000-01-01, 2000-02-01)'),
+  (11, '[2000-01-01, 2000-02-01)'),
+  (11, '[2000-02-01, 2000-03-01)'),
+  (12, '[2000-01-01, 2000-02-01)');
+
+select * from parttmp order by id, valid_at;
+select * from parttmp_1_to_10 order by id, valid_at;
+select * from parttmp_11_to_20 order by id, valid_at;
+
+update parttmp set valid_at = valid_at * '[2000-01-15,2000-02-15)' where id = 1;
+
+select * from parttmp order by id, valid_at;
+select * from parttmp_1_to_10 order by id, valid_at;
+select * from parttmp_11_to_20 order by id, valid_at;
+
+-- make sure the excluson constraint excludes:
+insert into parttmp (id, valid_at) values
+  (2, '[2000-01-15, 2000-02-01)');
+
+drop table parttmp;
+
+-- should fail with a good error message:
+create table parttmp (id int, valid_at daterange, exclude using gist (id with <>, valid_at with &&)) partition by range (id);

doc/src/sgml/ddl.sgml

@@ -4216,11 +4216,13 @@ ALTER INDEX measurement_city_id_logdate_key
 
      <listitem>
       <para>
-       There is no way to create an exclusion constraint spanning the
-       whole partitioned table.  It is only possible to put such a
-       constraint on each leaf partition individually.  Again, this
-       limitation stems from not being able to enforce cross-partition
-       restrictions.
+       Similarly an exclusion constraint must include all the
+       partition key columns. Furthermore the constraint must compare those
+       columns for equality (not e.g. <literal>&amp;&amp;</literal>).
+       Again, this limitation stems from not being able to enforce
+       cross-partition restrictions. The constraint may include additional
+       columns that aren't part of the partition key, and it may compare
+       those with any operators you like.
       </para>
      </listitem>
 

src/backend/commands/indexcmds.c

@@ -712,11 +712,6 @@ DefineIndex(Oid relationId,
 					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 					 errmsg("cannot create index on partitioned table \"%s\" concurrently",
 							RelationGetRelationName(rel))));
-		if (stmt->excludeOpNames)
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("cannot create exclusion constraints on partitioned table \"%s\"",
-							RelationGetRelationName(rel))));
 	}
 
 	/*
@@ -923,15 +918,16 @@ DefineIndex(Oid relationId,
 		index_check_primary_key(rel, indexInfo, is_alter_table, stmt);
 
 	/*
-	 * If this table is partitioned and we're creating a unique index or a
-	 * primary key, make sure that the partition key is a subset of the
-	 * index's columns.  Otherwise it would be possible to violate uniqueness
-	 * by putting values that ought to be unique in different partitions.
+	 * If this table is partitioned and we're creating a unique index, primary
+	 * key, or exclusion constraint, make sure that the partition key is a
+	 * subset of the index's columns.  Otherwise it would be possible to
+	 * violate uniqueness by putting values that ought to be unique in
+	 * different partitions.
 	 *
 	 * We could lift this limitation if we had global indexes, but those have
 	 * their own problems, so this is a useful feature combination.
 	 */
-	if (partitioned && (stmt->unique || stmt->primary))
+	if (partitioned && (stmt->unique || stmt->excludeOpNames))
 	{
 		PartitionKey key = RelationGetPartitionKey(rel);
 		const char *constraint_type;
@@ -941,7 +937,7 @@ DefineIndex(Oid relationId,
 			constraint_type = "PRIMARY KEY";
 		else if (stmt->unique)
 			constraint_type = "UNIQUE";
-		else if (stmt->excludeOpNames != NIL)
+		else if (stmt->excludeOpNames)
 			constraint_type = "EXCLUDE";
 		else
 		{
@@ -984,11 +980,11 @@ DefineIndex(Oid relationId,
 			 * We'll need to be able to identify the equality operators
 			 * associated with index columns, too.  We know what to do with
 			 * btree opclasses; if there are ever any other index types that
-			 * support unique indexes, this logic will need extension.
+			 * support unique indexes, this logic will need extension. But if
+			 * we have an exclusion constraint, it already knows the
+			 * operators, so we don't have to infer them.
 			 */
-			if (accessMethodId == BTREE_AM_OID)
-				eq_strategy = BTEqualStrategyNumber;
-			else
+			if (stmt->unique && accessMethodId != BTREE_AM_OID)
 				ereport(ERROR,
 						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 						 errmsg("cannot match partition key to an index using access method \"%s\"",
@@ -1019,17 +1015,38 @@ DefineIndex(Oid relationId,
 															&idx_opfamily,
 															&idx_opcintype))
 					{
-						Oid			idx_eqop;
+						Oid			idx_eqop = InvalidOid;
+
+						if (stmt->unique)
+							idx_eqop = get_opfamily_member(idx_opfamily,
+														   idx_opcintype,
+														   idx_opcintype,
+														   BTEqualStrategyNumber);
+						else if (stmt->excludeOpNames)
+							idx_eqop = indexInfo->ii_ExclusionOps[j];
+						Assert(idx_eqop);
 
-						idx_eqop = get_opfamily_member(idx_opfamily,
-													   idx_opcintype,
-													   idx_opcintype,
-													   eq_strategy);
 						if (ptkey_eqop == idx_eqop)
 						{
 							found = true;
 							break;
 						}
+						else if (stmt->excludeOpNames)
+						{
+							/*
+							 * We found a match, but it's not an equality
+							 * operator. Instead of failing below with an
+							 * error message about a missing column, fail now
+							 * and explain that the operator is wrong.
+							 */
+							Form_pg_attribute att = TupleDescAttr(RelationGetDescr(rel), key->partattrs[i] - 1);
+
+							ereport(ERROR,
+									(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+									 errmsg("cannot match partition key to index on column \"%s\" using non-equal operator \"%s\"",
+											NameStr(att->attname),
+											get_opname(indexInfo->ii_ExclusionOps[j]))));
+						}
 					}
 				}
 			}
@@ -1101,7 +1118,7 @@ DefineIndex(Oid relationId,
 			constraint_type = "PRIMARY KEY";
 		else if (stmt->unique)
 			constraint_type = "UNIQUE";
-		else if (stmt->excludeOpNames != NIL)
+		else if (stmt->excludeOpNames)
 			constraint_type = "EXCLUDE";
 		else
 		{

src/backend/parser/parse_utilcmd.c

@@ -900,12 +900,6 @@ transformTableConstraint(CreateStmtContext *cxt, Constraint *constraint)
 						 errmsg("exclusion constraints are not supported on foreign tables"),
 						 parser_errposition(cxt->pstate,
 											constraint->location)));
-			if (cxt->ispartitioned)
-				ereport(ERROR,
-						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-						 errmsg("exclusion constraints are not supported on partitioned tables"),
-						 parser_errposition(cxt->pstate,
-											constraint->location)));
 			cxt->ixconstraints = lappend(cxt->ixconstraints, constraint);
 			break;
 

src/test/regress/expected/alter_table.out

@@ -3834,16 +3834,11 @@ Referenced by:
     TABLE "ataddindex" CONSTRAINT "ataddindex_ref_id_fkey" FOREIGN KEY (ref_id) REFERENCES ataddindex(id)
 
 DROP TABLE ataddindex;
--- unsupported constraint types for partitioned tables
+-- cannot drop column that is part of the partition key
 CREATE TABLE partitioned (
 	a int,
 	b int
 ) PARTITION BY RANGE (a, (a+b+1));
-ALTER TABLE partitioned ADD EXCLUDE USING gist (a WITH &&);
-ERROR:  exclusion constraints are not supported on partitioned tables
-LINE 1: ALTER TABLE partitioned ADD EXCLUDE USING gist (a WITH &&);
-                                    ^
--- cannot drop column that is part of the partition key
 ALTER TABLE partitioned DROP COLUMN a;
 ERROR:  cannot drop column "a" because it is part of the partition key of relation "partitioned"
 ALTER TABLE partitioned ALTER COLUMN a TYPE char(5);

src/test/regress/expected/create_table.out

@@ -153,14 +153,6 @@ CREATE TABLE partitioned (
 	a2 int
 ) PARTITION BY LIST (a1, a2);	-- fail
 ERROR:  cannot use "list" partition strategy with more than one column
--- unsupported constraint type for partitioned tables
-CREATE TABLE partitioned (
-	a int,
-	EXCLUDE USING gist (a WITH &&)
-) PARTITION BY RANGE (a);
-ERROR:  exclusion constraints are not supported on partitioned tables
-LINE 3:  EXCLUDE USING gist (a WITH &&)
-         ^
 -- prevent using prohibited expressions in the key
 CREATE FUNCTION retset (a int) RETURNS SETOF int AS $$ SELECT 1; $$ LANGUAGE SQL IMMUTABLE;
 CREATE TABLE partitioned (