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

8 files changed, 154 insertions, 67 deletions

diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index 02250ae74be..baf3e6e57a5 100644
--- a/src/backend/commands/indexcmds.c
+++ b/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
 		{
diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
index d67580fc77a..e48e9e99d36 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/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;
 
diff --git a/src/test/regress/expected/alter_table.out b/src/test/regress/expected/alter_table.out
index 05351cb1a43..cd814ff321c 100644
--- a/src/test/regress/expected/alter_table.out
+++ b/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);
diff --git a/src/test/regress/expected/create_table.out b/src/test/regress/expected/create_table.out
index 1c3ef2b05a8..2a0902ece24 100644
--- a/src/test/regress/expected/create_table.out
+++ b/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 (
diff --git a/src/test/regress/expected/indexing.out b/src/test/regress/expected/indexing.out
index 3e5645c2ab6..2be8ffa7ec4 100644
--- a/src/test/regress/expected/indexing.out
+++ b/src/test/regress/expected/indexing.out
@@ -986,11 +986,32 @@ DETAIL:  PRIMARY KEY constraint on table "idxpart" lacks column "a" which is par
 -- OK if you use them in some other order
 create table idxpart (a int, b int, c text, primary key  (a, b, c)) partition by range (b, c, a);
 drop table idxpart;
--- not other types of index-based constraints
-create table idxpart (a int, exclude (a with = )) partition by range (a);
-ERROR:  exclusion constraints are not supported on partitioned tables
-LINE 1: create table idxpart (a int, exclude (a with = )) partition ...
-                                     ^
+-- OK to add an exclusion constraint if partitioning by its equal column
+create table idxpart (a int4range, exclude USING GIST (a with = )) partition by range (a);
+drop table idxpart;
+-- OK more than one equal column
+create table idxpart (a int4range, b int4range, exclude USING GIST (a with =, b with =)) partition by range (a, b);
+drop table idxpart;
+-- OK with more than one equal column: constraint is a proper superset of partition key
+create table idxpart (a int4range, b int4range, exclude USING GIST (a with =, b with =)) partition by range (a);
+drop table idxpart;
+-- Not OK more than one equal column: partition keys are a proper superset of constraint
+create table idxpart (a int4range, b int4range, exclude USING GIST (a with = )) partition by range (a, b);
+ERROR:  unique constraint on partitioned table must include all partitioning columns
+DETAIL:  EXCLUDE constraint on table "idxpart" lacks column "b" which is part of the partition key.
+-- Not OK with just -|-
+create table idxpart (a int4range, exclude USING GIST (a with -|- )) partition by range (a);
+ERROR:  cannot match partition key to index on column "a" using non-equal operator "-|-"
+-- OK with equals and &&, and equals is the partition key
+create table idxpart (a int4range, b int4range, exclude USING GIST (a with =, b with &&)) partition by range (a);
+drop table idxpart;
+-- Not OK with equals and &&, and equals is not the partition key
+create table idxpart (a int4range, b int4range, c int4range, exclude USING GIST (b with =, c with &&)) partition by range (a);
+ERROR:  unique constraint on partitioned table must include all partitioning columns
+DETAIL:  EXCLUDE constraint on table "idxpart" lacks column "a" which is part of the partition key.
+-- OK more than one equal column and a && column
+create table idxpart (a int4range, b int4range, c int4range, exclude USING GIST (a with =, b with =, c with &&)) partition by range (a, b);
+drop table idxpart;
 -- no expressions in partition key for PK/UNIQUE
 create table idxpart (a int primary key, b int) partition by range ((b + a));
 ERROR:  unsupported PRIMARY KEY constraint with partition key definition
@@ -1047,12 +1068,42 @@ Indexes:
 Number of partitions: 0
 
 drop table idxpart;
--- Exclusion constraints cannot be added
-create table idxpart (a int, b int) partition by range (a);
-alter table idxpart add exclude (a with =);
-ERROR:  exclusion constraints are not supported on partitioned tables
-LINE 1: alter table idxpart add exclude (a with =);
-                                ^
+-- Exclusion constraints can be added if partitioning by their equal column
+create table idxpart (a int4range, b int4range) partition by range (a);
+alter table idxpart add exclude USING GIST (a with =);
+drop table idxpart;
+-- OK more than one equal column
+create table idxpart (a int4range, b int4range) partition by range (a, b);
+alter table idxpart add exclude USING GIST (a with =, b with =);
+drop table idxpart;
+-- OK with more than one equal column: constraint is a proper superset of partition key
+create table idxpart (a int4range, b int4range) partition by range (a);
+alter table idxpart add exclude USING GIST (a with =, b with =);
+drop table idxpart;
+-- Not OK more than one equal column: partition keys are a proper superset of constraint
+create table idxpart (a int4range, b int4range) partition by range (a, b);
+alter table idxpart add exclude USING GIST (a with =);
+ERROR:  unique constraint on partitioned table must include all partitioning columns
+DETAIL:  EXCLUDE constraint on table "idxpart" lacks column "b" which is part of the partition key.
+drop table idxpart;
+-- Not OK with just -|-
+create table idxpart (a int4range, b int4range) partition by range (a, b);
+alter table idxpart add exclude USING GIST (a with -|-);
+ERROR:  cannot match partition key to index on column "a" using non-equal operator "-|-"
+drop table idxpart;
+-- OK with equals and &&, and equals is the partition key
+create table idxpart (a int4range, b int4range) partition by range (a);
+alter table idxpart add exclude USING GIST (a with =, b with &&);
+drop table idxpart;
+-- Not OK with equals and &&, and equals is not the partition key
+create table idxpart (a int4range, b int4range, c int4range) partition by range (a);
+alter table idxpart add exclude USING GIST (b with =, c with &&);
+ERROR:  unique constraint on partitioned table must include all partitioning columns
+DETAIL:  EXCLUDE constraint on table "idxpart" lacks column "a" which is part of the partition key.
+drop table idxpart;
+-- OK more than one equal column and a && column
+create table idxpart (a int4range, b int4range, c int4range) partition by range (a, b);
+alter table idxpart add exclude USING GIST (a with =, b with =, c with &&);
 drop table idxpart;
 -- When (sub)partitions are created, they also contain the constraint
 create table idxpart (a int, b int, primary key (a, b)) partition by range (a, b);
diff --git a/src/test/regress/sql/alter_table.sql b/src/test/regress/sql/alter_table.sql
index 58ea20ac3dc..ff8c4984191 100644
--- a/src/test/regress/sql/alter_table.sql
+++ b/src/test/regress/sql/alter_table.sql
@@ -2342,14 +2342,11 @@ ALTER TABLE ataddindex
 \d ataddindex
 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 &&);
-
--- cannot drop column that is part of the partition key
 ALTER TABLE partitioned DROP COLUMN a;
 ALTER TABLE partitioned ALTER COLUMN a TYPE char(5);
 ALTER TABLE partitioned DROP COLUMN b;
diff --git a/src/test/regress/sql/create_table.sql b/src/test/regress/sql/create_table.sql
index 93ccf77d4a1..82ada476618 100644
--- a/src/test/regress/sql/create_table.sql
+++ b/src/test/regress/sql/create_table.sql
@@ -106,12 +106,6 @@ CREATE TABLE partitioned (
 	a2 int
 ) PARTITION BY LIST (a1, a2);	-- fail
 
--- unsupported constraint type for partitioned tables
-CREATE TABLE partitioned (
-	a int,
-	EXCLUDE USING gist (a WITH &&)
-) PARTITION BY RANGE (a);
-
 -- prevent using prohibited expressions in the key
 CREATE FUNCTION retset (a int) RETURNS SETOF int AS $$ SELECT 1; $$ LANGUAGE SQL IMMUTABLE;
 CREATE TABLE partitioned (
diff --git a/src/test/regress/sql/indexing.sql b/src/test/regress/sql/indexing.sql
index d6e5a06d95a..b69c41832ca 100644
--- a/src/test/regress/sql/indexing.sql
+++ b/src/test/regress/sql/indexing.sql
@@ -483,8 +483,27 @@ create table idxpart (a int, b int primary key) partition by range (b, a);
 create table idxpart (a int, b int, c text, primary key  (a, b, c)) partition by range (b, c, a);
 drop table idxpart;
 
--- not other types of index-based constraints
-create table idxpart (a int, exclude (a with = )) partition by range (a);
+-- OK to add an exclusion constraint if partitioning by its equal column
+create table idxpart (a int4range, exclude USING GIST (a with = )) partition by range (a);
+drop table idxpart;
+-- OK more than one equal column
+create table idxpart (a int4range, b int4range, exclude USING GIST (a with =, b with =)) partition by range (a, b);
+drop table idxpart;
+-- OK with more than one equal column: constraint is a proper superset of partition key
+create table idxpart (a int4range, b int4range, exclude USING GIST (a with =, b with =)) partition by range (a);
+drop table idxpart;
+-- Not OK more than one equal column: partition keys are a proper superset of constraint
+create table idxpart (a int4range, b int4range, exclude USING GIST (a with = )) partition by range (a, b);
+-- Not OK with just -|-
+create table idxpart (a int4range, exclude USING GIST (a with -|- )) partition by range (a);
+-- OK with equals and &&, and equals is the partition key
+create table idxpart (a int4range, b int4range, exclude USING GIST (a with =, b with &&)) partition by range (a);
+drop table idxpart;
+-- Not OK with equals and &&, and equals is not the partition key
+create table idxpart (a int4range, b int4range, c int4range, exclude USING GIST (b with =, c with &&)) partition by range (a);
+-- OK more than one equal column and a && column
+create table idxpart (a int4range, b int4range, c int4range, exclude USING GIST (a with =, b with =, c with &&)) partition by range (a, b);
+drop table idxpart;
 
 -- no expressions in partition key for PK/UNIQUE
 create table idxpart (a int primary key, b int) partition by range ((b + a));
@@ -506,9 +525,37 @@ alter table idxpart add unique (b, a);		-- this works
 \d idxpart
 drop table idxpart;
 
--- Exclusion constraints cannot be added
-create table idxpart (a int, b int) partition by range (a);
-alter table idxpart add exclude (a with =);
+-- Exclusion constraints can be added if partitioning by their equal column
+create table idxpart (a int4range, b int4range) partition by range (a);
+alter table idxpart add exclude USING GIST (a with =);
+drop table idxpart;
+-- OK more than one equal column
+create table idxpart (a int4range, b int4range) partition by range (a, b);
+alter table idxpart add exclude USING GIST (a with =, b with =);
+drop table idxpart;
+-- OK with more than one equal column: constraint is a proper superset of partition key
+create table idxpart (a int4range, b int4range) partition by range (a);
+alter table idxpart add exclude USING GIST (a with =, b with =);
+drop table idxpart;
+-- Not OK more than one equal column: partition keys are a proper superset of constraint
+create table idxpart (a int4range, b int4range) partition by range (a, b);
+alter table idxpart add exclude USING GIST (a with =);
+drop table idxpart;
+-- Not OK with just -|-
+create table idxpart (a int4range, b int4range) partition by range (a, b);
+alter table idxpart add exclude USING GIST (a with -|-);
+drop table idxpart;
+-- OK with equals and &&, and equals is the partition key
+create table idxpart (a int4range, b int4range) partition by range (a);
+alter table idxpart add exclude USING GIST (a with =, b with &&);
+drop table idxpart;
+-- Not OK with equals and &&, and equals is not the partition key
+create table idxpart (a int4range, b int4range, c int4range) partition by range (a);
+alter table idxpart add exclude USING GIST (b with =, c with &&);
+drop table idxpart;
+-- OK more than one equal column and a && column
+create table idxpart (a int4range, b int4range, c int4range) partition by range (a, b);
+alter table idxpart add exclude USING GIST (a with =, b with =, c with &&);
 drop table idxpart;
 
 -- When (sub)partitions are created, they also contain the constraint