Mark hash distributed tables with replication factor = 1 as streaming replicated tables (repmodel=s).

This works only with `create_distributed_table` call.

src/backend/distributed/commands/create_distributed_table.c

@@ -79,8 +79,7 @@ static void InsertIntoPgDistPartition(Oid relationId, char distributionMethod,
 									  char replicationModel);
 static void CreateHashDistributedTable(Oid relationId, char *distributionColumnName,
 									   char *colocateWithTableName,
-									   int shardCount, int replicationFactor,
+									   int shardCount, int replicationFactor);
-									   char replicationModel);
 static Oid ColumnType(Oid relationId, char *columnName);
 
 
@@ -172,8 +171,7 @@ create_distributed_table(PG_FUNCTION_ARGS)
 	/* use configuration values for shard count and shard replication factor */
 	CreateHashDistributedTable(relationId, distributionColumnName,
 							   colocateWithTableName, ShardCount,
-							   ShardReplicationFactor,
+							   ShardReplicationFactor);
-							   REPLICATION_MODEL_COORDINATOR);
 
 	PG_RETURN_VOID();
 }
@@ -953,17 +951,28 @@ CreateTruncateTrigger(Oid relationId)
 static void
 CreateHashDistributedTable(Oid relationId, char *distributionColumnName,
 						   char *colocateWithTableName, int shardCount,
-						   int replicationFactor, char replicationModel)
+						   int replicationFactor)
 {
 	Relation distributedRelation = NULL;
 	Relation pgDistColocation = NULL;
 	uint32 colocationId = INVALID_COLOCATION_ID;
 	Oid sourceRelationId = InvalidOid;
 	Oid distributionColumnType = InvalidOid;
+	char replicationModel = 0;
 
 	/* get an access lock on the relation to prevent DROP TABLE and ALTER TABLE */
 	distributedRelation = relation_open(relationId, AccessShareLock);
 
+	/* all hash-distributed tables with repfactor=1 are treated as MX tables */
+	if (replicationFactor == 1)
+	{
+		replicationModel = REPLICATION_MODEL_STREAMING;
+	}
+	else
+	{
+		replicationModel = REPLICATION_MODEL_COORDINATOR;
+	}
+
 	/*
 	 * Get an exclusive lock on the colocation system catalog. Therefore, we
 	 * can be sure that there will no modifications on the colocation table
@@ -1004,7 +1013,7 @@ CreateHashDistributedTable(Oid relationId, char *distributionColumnName,
 
 	/* create distributed table metadata */
 	ConvertToDistributedTable(relationId, distributionColumnName, DISTRIBUTE_BY_HASH,
-							  colocationId, REPLICATION_MODEL_COORDINATOR);
+							  colocationId, replicationModel);
 
 	/* create shards */
 	if (sourceRelationId != InvalidOid)

src/test/regress/expected/multi_colocation_utils.out

@@ -371,6 +371,8 @@ SELECT create_distributed_table('table2_groupB', 'id');
  
 (1 row)
 
+UPDATE pg_dist_partition SET repmodel='c' WHERE logicalrelid='table1_groupB'::regclass;
+UPDATE pg_dist_partition SET repmodel='c' WHERE logicalrelid='table2_groupB'::regclass;
 -- revert back to default shard replication factor
 SET citus.shard_replication_factor to DEFAULT;
 -- change partition column type

src/test/regress/expected/multi_create_table.out

@@ -137,3 +137,53 @@ SELECT master_create_distributed_table('supplier_single_shard', 's_suppkey', 'ap
  
 (1 row)
 
+-- Show that when a hash distributed table with replication factor=1 is created, it 
+-- automatically marked as streaming replicated
+SET citus.shard_replication_factor TO 1;
+CREATE TABLE mx_table_test (col1 int, col2 text);
+SELECT create_distributed_table('mx_table_test', 'col1');
+ create_distributed_table 
+--------------------------
+ 
+(1 row)
+
+SELECT repmodel FROM pg_dist_partition WHERE logicalrelid='mx_table_test'::regclass;
+ repmodel 
+----------
+ s
+(1 row)
+
+DROP TABLE mx_table_test; 
+-- Show that it is not possible to create an mx table with the old 
+-- master_create_distributed_table function
+CREATE TABLE mx_table_test (col1 int, col2 text);
+SELECT master_create_distributed_table('mx_table_test', 'col1', 'hash');
+ master_create_distributed_table 
+---------------------------------
+ 
+(1 row)
+
+SELECT repmodel FROM pg_dist_partition WHERE logicalrelid='mx_table_test'::regclass;
+ repmodel 
+----------
+ c
+(1 row)
+
+DROP TABLE mx_table_test;
+-- Show that when replication factor > 1 the table is created as coordinator-replicated
+SET citus.shard_replication_factor TO 2;
+CREATE TABLE mx_table_test (col1 int, col2 text);
+SELECT create_distributed_table('mx_table_test', 'col1');
+ create_distributed_table 
+--------------------------
+ 
+(1 row)
+
+SELECT repmodel FROM pg_dist_partition WHERE logicalrelid='mx_table_test'::regclass;
+ repmodel 
+----------
+ c
+(1 row)
+
+DROP TABLE mx_table_test; 
+SET citus.shard_replication_factor TO default;

src/test/regress/sql/multi_colocation_utils.sql

@@ -175,6 +175,9 @@ SELECT create_distributed_table('table1_groupB', 'id');
 CREATE TABLE table2_groupB ( id int );
 SELECT create_distributed_table('table2_groupB', 'id');
 
+UPDATE pg_dist_partition SET repmodel='c' WHERE logicalrelid='table1_groupB'::regclass;
+UPDATE pg_dist_partition SET repmodel='c' WHERE logicalrelid='table2_groupB'::regclass;
+
 -- revert back to default shard replication factor
 SET citus.shard_replication_factor to DEFAULT;
 

src/test/regress/sql/multi_create_table.sql

@@ -111,3 +111,28 @@ CREATE TABLE supplier_single_shard
   	s_comment varchar(101) not null
 );
 SELECT master_create_distributed_table('supplier_single_shard', 's_suppkey', 'append');
+
+-- Show that when a hash distributed table with replication factor=1 is created, it 
+-- automatically marked as streaming replicated
+SET citus.shard_replication_factor TO 1;
+
+CREATE TABLE mx_table_test (col1 int, col2 text);
+SELECT create_distributed_table('mx_table_test', 'col1');
+SELECT repmodel FROM pg_dist_partition WHERE logicalrelid='mx_table_test'::regclass;
+DROP TABLE mx_table_test; 
+
+-- Show that it is not possible to create an mx table with the old 
+-- master_create_distributed_table function
+CREATE TABLE mx_table_test (col1 int, col2 text);
+SELECT master_create_distributed_table('mx_table_test', 'col1', 'hash');
+SELECT repmodel FROM pg_dist_partition WHERE logicalrelid='mx_table_test'::regclass;
+DROP TABLE mx_table_test;
+
+-- Show that when replication factor > 1 the table is created as coordinator-replicated
+SET citus.shard_replication_factor TO 2;
+CREATE TABLE mx_table_test (col1 int, col2 text);
+SELECT create_distributed_table('mx_table_test', 'col1');
+SELECT repmodel FROM pg_dist_partition WHERE logicalrelid='mx_table_test'::regclass;
+DROP TABLE mx_table_test; 
+
+SET citus.shard_replication_factor TO default;