Refactor CreateDistributedTable() (#6742)

Split the main logic that allows creating a Citus table into the
internal function CreateCitusTable().

Old CreateDistributedTable() function was assuming that it's creating
a reference table when the distribution method is DISTRIBUTE_BY_NONE.
However, soon this won't be the case when adding support for creating
single-shard distributed tables because their distribution method would
also be the same.

Now the internal method CreateCitusTable() doesn't make any assumptions
about table's replication model or such. Instead, it expects callers to
properly set all such metadata bits.

Even more, some of the parameters the old CreateDistributedTable() takes
 --such as the shard count-- were not meaningful for a reference table,
and would be the same as for new table type.

src/backend/distributed/commands/alter_table.c

@@ -1348,8 +1348,7 @@ CreateCitusTableLike(TableConversionState *con)
 	}
 	else if (IsCitusTableType(con->relationId, REFERENCE_TABLE))
 	{
-		CreateDistributedTable(con->newRelationId, NULL, DISTRIBUTE_BY_NONE, 0, false,
-							   NULL);
+		CreateReferenceTable(con->newRelationId);
 	}
 	else if (IsCitusTableType(con->relationId, CITUS_LOCAL_TABLE))
 	{

src/backend/distributed/commands/create_distributed_table.c

@@ -106,11 +106,17 @@ static void CreateDistributedTableConcurrently(Oid relationId,
 											   char *colocateWithTableName,
 											   int shardCount,
 											   bool shardCountIsStrict);
-static char DecideReplicationModel(char distributionMethod, char *colocateWithTableName);
+static char DecideDistTableReplicationModel(char distributionMethod,
+											char *colocateWithTableName);
 static List * HashSplitPointsForShardList(List *shardList);
 static List * HashSplitPointsForShardCount(int shardCount);
 static List * WorkerNodesForShardList(List *shardList);
 static List * RoundRobinWorkerNodeList(List *workerNodeList, int listLength);
+static void CreateCitusTable(Oid relationId, char *distributionColumnName,
+							 char distributionMethod,
+							 int shardCount, bool shardCountIsStrict,
+							 char *colocateWithTableName,
+							 char replicationModel);
 static void CreateHashDistributedTableShards(Oid relationId, int shardCount,
 											 Oid colocatedTableId, bool localTableEmpty);
 static uint32 ColocationIdForNewTable(Oid relationId, Var *distributionColumn,
@@ -377,8 +383,8 @@ CreateDistributedTableConcurrently(Oid relationId, char *distributionColumnName,
 
 	EnsureForeignKeysForDistributedTableConcurrently(relationId);
 
-	char replicationModel = DecideReplicationModel(distributionMethod,
-												   colocateWithTableName);
+	char replicationModel = DecideDistTableReplicationModel(distributionMethod,
+															colocateWithTableName);
 
 	/*
 	 * we fail transaction before local table conversion if the table could not be colocated with
@@ -622,8 +628,8 @@ static void
 EnsureColocateWithTableIsValid(Oid relationId, char distributionMethod,
 							   char *distributionColumnName, char *colocateWithTableName)
 {
-	char replicationModel = DecideReplicationModel(distributionMethod,
-												   colocateWithTableName);
+	char replicationModel = DecideDistTableReplicationModel(distributionMethod,
+															colocateWithTableName);
 
 	/*
 	 * we fail transaction before local table conversion if the table could not be colocated with
@@ -860,9 +866,6 @@ create_reference_table(PG_FUNCTION_ARGS)
 	CheckCitusVersion(ERROR);
 	Oid relationId = PG_GETARG_OID(0);
 
-	char *colocateWithTableName = NULL;
-	char *distributionColumnName = NULL;
-
 	EnsureCitusTableCanBeCreated(relationId);
 
 	/* enable create_reference_table on an empty node */
@@ -895,8 +898,7 @@ create_reference_table(PG_FUNCTION_ARGS)
 						errdetail("There are no active worker nodes.")));
 	}
 
-	CreateDistributedTable(relationId, distributionColumnName, DISTRIBUTE_BY_NONE,
-						   ShardCount, false, colocateWithTableName);
+	CreateReferenceTable(relationId);
 	PG_RETURN_VOID();
 }
 
@@ -951,17 +953,61 @@ EnsureRelationExists(Oid relationId)
 
 
 /*
- * CreateDistributedTable creates distributed table in the given configuration.
+ * CreateReferenceTable is a wrapper around CreateCitusTable that creates a
+ * distributed table.
+ */
+void
+CreateDistributedTable(Oid relationId, char *distributionColumnName,
+					   char distributionMethod,
+					   int shardCount, bool shardCountIsStrict,
+					   char *colocateWithTableName)
+{
+	Assert(distributionMethod != DISTRIBUTE_BY_NONE);
+
+	char replicationModel = DecideDistTableReplicationModel(distributionMethod,
+															colocateWithTableName);
+	CreateCitusTable(relationId, distributionColumnName,
+					 distributionMethod, shardCount,
+					 shardCountIsStrict, colocateWithTableName,
+					 replicationModel);
+}
+
+
+/*
+ * CreateReferenceTable is a wrapper around CreateCitusTable that creates a
+ * reference table.
+ */
+void
+CreateReferenceTable(Oid relationId)
+{
+	char *distributionColumnName = NULL;
+	char distributionMethod = DISTRIBUTE_BY_NONE;
+	int shardCount = 1;
+	bool shardCountIsStrict = true;
+	char *colocateWithTableName = NULL;
+	char replicationModel = REPLICATION_MODEL_2PC;
+	CreateCitusTable(relationId, distributionColumnName,
+					 distributionMethod, shardCount,
+					 shardCountIsStrict, colocateWithTableName,
+					 replicationModel);
+}
+
+
+/*
+ * CreateCitusTable is the internal method that creates a Citus table in
+ * given configuration.
+ *
  * This functions contains all necessary logic to create distributed tables. It
  * performs necessary checks to ensure distributing the table is safe. If it is
  * safe to distribute the table, this function creates distributed table metadata,
  * creates shards and copies local data to shards. This function also handles
  * partitioned tables by distributing its partitions as well.
  */
-void
-CreateDistributedTable(Oid relationId, char *distributionColumnName,
-					   char distributionMethod, int shardCount,
-					   bool shardCountIsStrict, char *colocateWithTableName)
+static void
+CreateCitusTable(Oid relationId, char *distributionColumnName,
+				 char distributionMethod, int shardCount,
+				 bool shardCountIsStrict, char *colocateWithTableName,
+				 char replicationModel)
 {
 	/*
 	 * EnsureTableNotDistributed errors out when relation is a citus table but
@@ -1022,9 +1068,6 @@ CreateDistributedTable(Oid relationId, char *distributionColumnName,
 
 	PropagatePrerequisiteObjectsForDistributedTable(relationId);
 
-	char replicationModel = DecideReplicationModel(distributionMethod,
-												   colocateWithTableName);
-
 	Var *distributionColumn = BuildDistributionKeyFromColumnName(relationId,
 																 distributionColumnName,
 																 NoLock);
@@ -1420,18 +1463,16 @@ DropFKeysRelationInvolvedWithTableType(Oid relationId, int tableTypeFlag)
 
 
 /*
- * DecideReplicationModel function decides which replication model should be
- * used depending on given distribution configuration.
+ * DecideDistTableReplicationModel function decides which replication model should be
+ * used for a distributed table depending on given distribution configuration.
  */
 static char
-DecideReplicationModel(char distributionMethod, char *colocateWithTableName)
+DecideDistTableReplicationModel(char distributionMethod, char *colocateWithTableName)
 {
-	if (distributionMethod == DISTRIBUTE_BY_NONE)
-	{
-		return REPLICATION_MODEL_2PC;
-	}
-	else if (pg_strncasecmp(colocateWithTableName, "default", NAMEDATALEN) != 0 &&
-			 !IsColocateWithNone(colocateWithTableName))
+	Assert(distributionMethod != DISTRIBUTE_BY_NONE);
+
+	if (!IsColocateWithDefault(colocateWithTableName) &&
+		!IsColocateWithNone(colocateWithTableName))
 	{
 		text *colocateWithTableNameText = cstring_to_text(colocateWithTableName);
 		Oid colocatedRelationId = ResolveRelationId(colocateWithTableNameText, false);

src/include/distributed/metadata_utility.h

@@ -325,6 +325,7 @@ extern void DeleteShardPlacementRow(uint64 placementId);
 extern void CreateDistributedTable(Oid relationId, char *distributionColumnName,
 								   char distributionMethod, int shardCount,
 								   bool shardCountIsStrict, char *colocateWithTableName);
+extern void CreateReferenceTable(Oid relationId);
 extern void CreateTruncateTrigger(Oid relationId);
 extern TableConversionReturn * UndistributeTable(TableConversionParameters *params);