source shardgroup id's from its own sequence

src/backend/distributed/operations/create_shards.c

@@ -194,9 +194,7 @@ CreateShardsWithRoundRobinPolicy(Oid distributedTableId, int32 shardCount,
 		int32 shardMinHashToken = PG_INT32_MIN + (shardIndex * hashTokenIncrement);
 		int32 shardMaxHashToken = shardMinHashToken + (hashTokenIncrement - 1);
 		uint64 shardId = GetNextShardId();
-
-		/* we use shardid of the first shard in a shardgroup as the shardgroupid */
-		int64 shardGroupId = (int64) shardId;
+		int64 shardGroupId = GetNextShardgroupId();
 
 		/* if we are at the last shard, make sure the max token value is INT_MAX */
 		if (shardIndex == (shardCount - 1))
@@ -399,7 +397,7 @@ CreateReferenceTableShard(Oid distributedTableId, Oid colocatedTableId,
 
 		/* get the next shard id */
 		uint64 shardId = GetNextShardId();
-		int64 shardGroupId = (int64) shardId;
+		int64 shardGroupId = GetNextShardgroupId();
 
 		StringInfoData shardgroupQuery = { 0 };
 		initStringInfo(&shardgroupQuery);

src/backend/distributed/operations/node_protocol.c

@@ -252,6 +252,30 @@ GetNextShardId()
 }
 
 
+int64
+GetNextShardgroupId()
+{
+	Oid savedUserId = InvalidOid;
+	int savedSecurityContext = 0;
+
+	text *sequenceName = cstring_to_text(SHARDGROUPID_SEQUENCE_NAME);
+	Oid sequenceId = ResolveRelationId(sequenceName, false);
+	Datum sequenceIdDatum = ObjectIdGetDatum(sequenceId);
+
+	GetUserIdAndSecContext(&savedUserId, &savedSecurityContext);
+	SetUserIdAndSecContext(CitusExtensionOwner(), SECURITY_LOCAL_USERID_CHANGE);
+
+	/* generate new and unique shardId from sequence */
+	Datum shardgroupIdDatum = DirectFunctionCall1(nextval_oid, sequenceIdDatum);
+
+	SetUserIdAndSecContext(savedUserId, savedSecurityContext);
+
+	int64 shardgroupId = DatumGetInt64(shardgroupIdDatum);
+
+	return shardgroupId;
+}
+
+
 /*
  * master_get_new_placementid is a user facing wrapper function around
  * GetNextPlacementId() which allocates and returns a unique placement id for the

src/backend/distributed/operations/shard_split.c

@@ -157,6 +157,7 @@ static void AddDummyShardEntryInMap(HTAB *mapOfPlacementToDummyShardList, uint32
 									targetNodeId,
 									ShardInterval *shardInterval);
 static uint64 GetNextShardIdForSplitChild(void);
+static int64 GetNextShardgroupIdForSplitChild(void);
 static void AcquireNonblockingSplitLock(Oid relationId);
 static List * GetWorkerNodesFromWorkerIds(List *nodeIdsForPlacementList);
 static void DropShardgroupMetadata(int64 shardgroupId);
@@ -1063,7 +1064,7 @@ CreateNewShardgroups(uint32 colocationId, ShardInterval *sampleInterval,
 		Datum splitPoint = (Datum) lfirst(splitPointCell);
 
 		Shardgroup *shardgroup = palloc0(sizeof(Shardgroup));
-		shardgroup->shardgroupId = (int64) GetNextShardIdForSplitChild();
+		shardgroup->shardgroupId = GetNextShardgroupIdForSplitChild();
 		shardgroup->colocationId = colocationId;
 		shardgroup->minShardValue = Int32GetDatum(currentSplitChildMinValue);
 		shardgroup->maxShardValue = splitPoint;
@@ -1080,7 +1081,7 @@ CreateNewShardgroups(uint32 colocationId, ShardInterval *sampleInterval,
 	 */
 
 	Shardgroup *shardgroup = palloc0(sizeof(Shardgroup));
-	shardgroup->shardgroupId = (int64) GetNextShardIdForSplitChild();
+	shardgroup->shardgroupId = GetNextShardgroupIdForSplitChild();
 	shardgroup->colocationId = colocationId;
 	shardgroup->minShardValue = Int32GetDatum(currentSplitChildMinValue);
 	shardgroup->maxShardValue = splitParentMaxValue;
@@ -2228,3 +2229,36 @@ GetNextShardIdForSplitChild()
 
 	return shardId;
 }
+
+
+static int64
+GetNextShardgroupIdForSplitChild()
+{
+	StringInfo nextValueCommand = makeStringInfo();
+	appendStringInfo(nextValueCommand, "SELECT nextval(%s);",
+					 quote_literal_cstr("pg_catalog.pg_dist_shardgroupid_seq"));
+
+	MultiConnection *connection =
+		GetConnectionForLocalQueriesOutsideTransaction(CitusExtensionOwnerName());
+
+	PGresult *result = NULL;
+	int queryResult = ExecuteOptionalRemoteCommand(connection, nextValueCommand->data,
+												   &result);
+	if (queryResult != RESPONSE_OKAY || !IsResponseOK(result) || PQntuples(result) != 1 ||
+		PQnfields(result) != 1)
+	{
+		PQclear(result);
+		ForgetResults(connection);
+		CloseConnection(connection);
+
+		ereport(ERROR, (errcode(ERRCODE_CONNECTION_FAILURE),
+						errmsg("Could not generate next shardgroup id while executing "
+							   "shard splits.")));
+	}
+
+	int64 shardgroupId = SafeStringToInt64(PQgetvalue(result, 0, 0 /* nodeId column*/));
+	PQclear(result);
+	ForgetResults(connection);
+
+	return shardgroupId;
+}

src/backend/distributed/operations/stage_protocol.c

@@ -186,7 +186,7 @@ master_create_empty_shard(PG_FUNCTION_ARGS)
 
 	CitusTableCacheEntry *tableEntry = LookupCitusTableCacheEntry(relationId);
 
-	int64 shardgroupId = (int64) shardId;
+	int64 shardgroupId = GetNextShardgroupId();
 	InsertShardGroupRow(shardgroupId, tableEntry->colocationId,
 						nullMinValue, nullMaxValue);
 

src/backend/distributed/sql/citus--11.2-1--11.3-1.sql

@@ -10,6 +10,11 @@ CREATE TABLE citus.pg_dist_shardgroup (
 );
 ALTER TABLE citus.pg_dist_shardgroup SET SCHEMA pg_catalog;
 
+CREATE SEQUENCE citus.pg_dist_shardgroupid_seq
+    MINVALUE 100000 -- TO BO DECIDED
+    NO CYCLE;
+ALTER SEQUENCE  citus.pg_dist_shardgroupid_seq SET SCHEMA pg_catalog;
+
 INSERT INTO pg_catalog.pg_dist_shardgroup
      SELECT min(shardid) as shardgroupid,
             colocationid,

src/include/distributed/coordinator_protocol.h

@@ -53,6 +53,7 @@
 #define TRANSFER_MODE_BLOCK_WRITES 'b'
 
 #define SHARDID_SEQUENCE_NAME "pg_dist_shardid_seq"
+#define SHARDGROUPID_SEQUENCE_NAME "pg_dist_shardgroupid_seq"
 #define PLACEMENTID_SEQUENCE_NAME "pg_dist_placement_placementid_seq"
 
 /* Remote call definitions to help with data staging and deletion */
@@ -221,6 +222,7 @@ extern bool IsCoordinator(void);
 
 /* Function declarations local to the distributed module */
 extern uint64 GetNextShardId(void);
+extern int64 GetNextShardgroupId(void);
 extern uint64 GetNextPlacementId(void);
 extern Oid ResolveRelationId(text *relationName, bool missingOk);
 extern List * GetFullTableCreationCommands(Oid relationId,