Adds citus.enable_local_reference_table_foreign_keys

When enabled any foreign keys between local tables and reference
tables supported by converting the local table to a citus local
table.

When the coordinator is not in the metadata, the logic is disabled
as foreign keys are not allowed in this configuration.

src/backend/distributed/commands/table.c

@@ -42,8 +42,13 @@
 #include "utils/syscache.h"
 
 
+/* controlled via GUC, should be accessed via GetEnableLocalReferenceForeignKeys() */
+bool EnableLocalReferenceForeignKeys = true;
+
+
 /* Local functions forward declarations for unsupported command checks */
 static void PostprocessCreateTableStmtForeignKeys(CreateStmt *createStatement);
+static bool ShouldEnableLocalReferenceForeignKeys(void);
 static void PostprocessCreateTableStmtPartitionOf(CreateStmt *createStatement,
 												  const char *queryString);
 static bool AlterTableDefinesFKeyBetweenPostgresAndNonDistTable(
@@ -84,6 +89,7 @@ static void SetInterShardDDLTaskRelationShardList(Task *task,
 												  ShardInterval *leftShardInterval,
 												  ShardInterval *rightShardInterval);
 
+
 /*
  * We need to run some of the commands sequentially if there is a foreign constraint
  * from/to reference table.
@@ -194,6 +200,14 @@ PostprocessCreateTableStmt(CreateStmt *createStatement, const char *queryString)
 static void
 PostprocessCreateTableStmtForeignKeys(CreateStmt *createStatement)
 {
+	if (!ShouldEnableLocalReferenceForeignKeys())
+	{
+		/*
+		 * Either the user disabled foreign keys from/to local/reference tables
+		 * or the coordinator is not in the metadata */
+		return;
+	}
+
 	/*
 	 * Relation must exist and it is already locked as standard process utility
 	 * is already executed.
@@ -227,6 +241,25 @@ PostprocessCreateTableStmtForeignKeys(CreateStmt *createStatement)
 }
 
 
+/*
+ * ShouldEnableLocalReferenceForeignKeys is a wrapper around getting the GUC
+ * EnableLocalReferenceForeignKeys. If the coordinator is not added
+ * to the metadata, the function returns false. Else, the function returns
+ * the value set by the user
+ *
+ */
+static bool
+ShouldEnableLocalReferenceForeignKeys(void)
+{
+	if (!EnableLocalReferenceForeignKeys)
+	{
+		return false;
+	}
+
+	return CoordinatorAddedAsWorkerNode();
+}
+
+
 /*
  * PostprocessCreateTableStmtPartitionOf processes CREATE TABLE ... PARTITION OF
  * statements and it checks if user creates the table as a partition of a distributed
@@ -412,8 +445,8 @@ PreprocessAlterTableStmt(Node *node, const char *alterTableCommand,
 		leftRelationId = IndexGetRelation(leftRelationId, missingOk);
 	}
 
-	if (processUtilityContext != PROCESS_UTILITY_SUBCOMMAND &&
+	if (ShouldEnableLocalReferenceForeignKeys() &&
-		CoordinatorAddedAsWorkerNode() &&
+		processUtilityContext != PROCESS_UTILITY_SUBCOMMAND &&
 		AlterTableDefinesFKeyBetweenPostgresAndNonDistTable(alterTableStatement))
 	{
 		/*

src/backend/distributed/shared_library_init.c

@@ -585,6 +585,18 @@ RegisterCitusConfigVariables(void)
 		GUC_STANDARD,
 		NULL, NULL, NULL);
 
+	DefineCustomBoolVariable(
+		"citus.enable_local_reference_table_foreign_keys",
+		gettext_noop("Enables foreign keys from/to local tables"),
+		gettext_noop("When enabled, foreign keys between local tables and reference "
+					 "tables supported."),
+		&EnableLocalReferenceForeignKeys,
+		true,
+		PGC_USERSET,
+		GUC_STANDARD,
+		NULL, NULL, NULL);
+
+
 	DefineCustomBoolVariable(
 		"citus.enable_single_hash_repartition_joins",
 		gettext_noop("Enables single hash repartitioning between hash "

src/include/distributed/commands.h

@@ -20,6 +20,11 @@
 #include "tcop/dest.h"
 #include "tcop/utility.h"
 
+
+/* controlled via GUC, should be accessed via EnableLocalReferenceForeignKeys() */
+extern bool EnableLocalReferenceForeignKeys;
+
+
 /*
  * DistributeObjectOps specifies handlers for node/object type pairs.
  * Instances of this type should all be declared in deparse.c.

src/test/regress/expected/fkeys_between_local_ref.out

@@ -391,6 +391,28 @@ BEGIN;
  reference_table_1 | n          | t
 (8 rows)
 
+ROLLBACK;
+BEGIN;
+  -- disable foreign keys to reference tables
+  SET LOCAL citus.enable_local_reference_table_foreign_keys TO false;
+  CREATE TABLE local_table_6 (col_1 INT PRIMARY KEY);
+  ALTER TABLE local_table_2 ADD CONSTRAINT fkey_11 FOREIGN KEY (col_1) REFERENCES reference_table_1(col_1) ON DELETE CASCADE;
+  CREATE TABLE local_table_5 (
+    col_1 INT UNIQUE REFERENCES local_table_6(col_1),
+    col_2 INT REFERENCES local_table_3(col_1),
+    FOREIGN KEY (col_1) REFERENCES local_table_5(col_1),
+    FOREIGN KEY (col_1) REFERENCES reference_table_1(col_1));
+  -- Now show none of local_table_5 & 6 to should be converted to citus local tables
+  -- as it is disabled
+  SELECT logicalrelid::text AS tablename, partmethod, repmodel FROM pg_dist_partition
+  WHERE logicalrelid::text IN (SELECT tablename FROM pg_tables WHERE schemaname='fkeys_between_local_ref')
+  ORDER BY tablename;
+     tablename     | partmethod | repmodel
+---------------------------------------------------------------------
+ distributed_table | h          | c
+ reference_table_1 | n          | t
+(2 rows)
+
 ROLLBACK;
 -- this errors out as we don't support creating citus local
 -- tables from partitioned tables

src/test/regress/sql/fkeys_between_local_ref.sql

@@ -285,6 +285,26 @@ BEGIN;
   ORDER BY tablename;
 ROLLBACK;
 
+BEGIN;
+  -- disable foreign keys to reference tables
+  SET LOCAL citus.enable_local_reference_table_foreign_keys TO false;
+  CREATE TABLE local_table_6 (col_1 INT PRIMARY KEY);
+
+  ALTER TABLE local_table_2 ADD CONSTRAINT fkey_11 FOREIGN KEY (col_1) REFERENCES reference_table_1(col_1) ON DELETE CASCADE;
+
+  CREATE TABLE local_table_5 (
+    col_1 INT UNIQUE REFERENCES local_table_6(col_1),
+    col_2 INT REFERENCES local_table_3(col_1),
+    FOREIGN KEY (col_1) REFERENCES local_table_5(col_1),
+    FOREIGN KEY (col_1) REFERENCES reference_table_1(col_1));
+
+  -- Now show none of local_table_5 & 6 to should be converted to citus local tables
+  -- as it is disabled
+  SELECT logicalrelid::text AS tablename, partmethod, repmodel FROM pg_dist_partition
+  WHERE logicalrelid::text IN (SELECT tablename FROM pg_tables WHERE schemaname='fkeys_between_local_ref')
+  ORDER BY tablename;
+ROLLBACK;
+
 -- this errors out as we don't support creating citus local
 -- tables from partitioned tables
 CREATE TABLE part_local_table (col_1 INT REFERENCES reference_table_1(col_1)) PARTITION BY RANGE (col_1);