Support foreign tables in MX

src/backend/distributed/commands/alter_table.c

@@ -368,7 +368,7 @@ UndistributeTable(TableConversionParameters *params)
 		EnsureTableNotReferencing(params->relationId, UNDISTRIBUTE_TABLE);
 		EnsureTableNotReferenced(params->relationId, UNDISTRIBUTE_TABLE);
 	}
-	EnsureTableNotForeign(params->relationId);
+
 	EnsureTableNotPartition(params->relationId);
 
 	if (PartitionedTable(params->relationId))
@@ -994,8 +994,7 @@ EnsureTableNotReferenced(Oid relationId, char conversionType)
 void
 EnsureTableNotForeign(Oid relationId)
 {
-	char relationKind = get_rel_relkind(relationId);
-	if (relationKind == RELKIND_FOREIGN_TABLE)
+	if (IsForeignTable(relationId))
 	{
 		ereport(ERROR, (errmsg("cannot complete operation "
 							   "because it is a foreign table")));
@@ -1063,7 +1062,7 @@ CreateTableConversion(TableConversionParameters *params)
 		BuildDistributionKeyFromColumnName(relation, con->distributionColumn);
 
 	con->originalAccessMethod = NULL;
-	if (!PartitionedTable(con->relationId))
+	if (!PartitionedTable(con->relationId) && !IsForeignTable(con->relationId))
 	{
 		HeapTuple amTuple = SearchSysCache1(AMOID, ObjectIdGetDatum(
 												relation->rd_rel->relam));
@@ -1305,7 +1304,7 @@ ReplaceTable(Oid sourceId, Oid targetId, List *justBeforeDropCommands,
 
 	StringInfo query = makeStringInfo();
 
-	if (!PartitionedTable(sourceId))
+	if (!PartitionedTable(sourceId) && !IsForeignTable(sourceId))
 	{
 		if (!suppressNoticeMessages)
 		{
@@ -1402,7 +1401,8 @@ ReplaceTable(Oid sourceId, Oid targetId, List *justBeforeDropCommands,
 	}
 
 	resetStringInfo(query);
-	appendStringInfo(query, "DROP TABLE %s CASCADE",
+	appendStringInfo(query, "DROP %sTABLE %s CASCADE",
+					 IsForeignTable(sourceId) ? "FOREIGN " : "",
 					 quote_qualified_identifier(schemaName, sourceName));
 	ExecuteQueryViaSPI(query->data, SPI_OK_UTILITY);
 

src/backend/distributed/commands/distribute_object_ops.c

@@ -797,6 +797,7 @@ GetDistributeObjectOps(Node *node)
 					return &Statistics_AlterObjectSchema;
 				}
 
+				case OBJECT_FOREIGN_TABLE:
 				case OBJECT_TABLE:
 				{
 					return &Table_AlterObjectSchema;

src/backend/distributed/commands/table.c

@@ -648,7 +648,7 @@ List *
 PostprocessAlterTableSchemaStmt(Node *node, const char *queryString)
 {
 	AlterObjectSchemaStmt *stmt = castNode(AlterObjectSchemaStmt, node);
-	Assert(stmt->objectType == OBJECT_TABLE);
+	Assert(stmt->objectType == OBJECT_TABLE || stmt->objectType == OBJECT_FOREIGN_TABLE);
 
 	/*
 	 * We will let Postgres deal with missing_ok
@@ -1054,7 +1054,8 @@ PreprocessAlterTableStmt(Node *node, const char *alterTableCommand,
 				 */
 				Assert(IsCitusTable(rightRelationId));
 			}
-			else if (attachedRelationKind == RELKIND_RELATION)
+			else if (attachedRelationKind == RELKIND_RELATION ||
+					 attachedRelationKind == RELKIND_FOREIGN_TABLE)
 			{
 				Assert(list_length(commandList) <= 1);
 
@@ -1761,7 +1762,7 @@ PreprocessAlterTableSchemaStmt(Node *node, const char *queryString,
 							   ProcessUtilityContext processUtilityContext)
 {
 	AlterObjectSchemaStmt *stmt = castNode(AlterObjectSchemaStmt, node);
-	Assert(stmt->objectType == OBJECT_TABLE);
+	Assert(stmt->objectType == OBJECT_TABLE || stmt->objectType == OBJECT_FOREIGN_TABLE);
 
 	if (stmt->relation == NULL)
 	{
@@ -2951,6 +2952,16 @@ ErrorIfUnsupportedAlterTableStmt(AlterTableStmt *alterTableStatement)
 				break;
 			}
 
+			case AT_GenericOptions:
+			{
+				if (IsForeignTable(relationId))
+				{
+					break;
+				}
+			}
+
+			/* fallthrough */
+
 			default:
 			{
 				ereport(ERROR,
@@ -3326,7 +3337,7 @@ ObjectAddress
 AlterTableSchemaStmtObjectAddress(Node *node, bool missing_ok)
 {
 	AlterObjectSchemaStmt *stmt = castNode(AlterObjectSchemaStmt, node);
-	Assert(stmt->objectType == OBJECT_TABLE);
+	Assert(stmt->objectType == OBJECT_TABLE || stmt->objectType == OBJECT_FOREIGN_TABLE);
 
 	const char *tableName = stmt->relation->relname;
 	Oid tableOid = InvalidOid;

src/backend/distributed/commands/truncate.c

@@ -267,15 +267,13 @@ ErrorIfUnsupportedTruncateStmt(TruncateStmt *truncateStatement)
 
 		ErrorIfIllegallyChangingKnownShard(relationId);
 
-		char relationKind = get_rel_relkind(relationId);
-		if (IsCitusTable(relationId) &&
-			relationKind == RELKIND_FOREIGN_TABLE)
+		if (IsCitusTable(relationId) && IsForeignTable(relationId))
 		{
 			ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 							errmsg("truncating distributed foreign tables is "
 								   "currently unsupported"),
-							errhint("Use citus_drop_all_shards to remove "
-									"foreign table's shards.")));
+							errhint("Consider undistributing table before TRUNCATE, "
+									"and then distribute or add to metadata again")));
 		}
 	}
 }

src/backend/distributed/commands/utility_hook.c

@@ -63,6 +63,7 @@
 #include "distributed/transmit.h"
 #include "distributed/version_compat.h"
 #include "distributed/worker_transaction.h"
+#include "foreign/foreign.h"
 #include "lib/stringinfo.h"
 #include "nodes/parsenodes.h"
 #include "nodes/pg_list.h"
@@ -98,6 +99,8 @@ static void DecrementUtilityHookCountersIfNecessary(Node *parsetree);
 static bool IsDropSchemaOrDB(Node *parsetree);
 static bool ShouldCheckUndistributeCitusLocalTables(void);
 static bool ShouldAddNewTableToMetadata(Node *parsetree);
+static bool ServerUsesPostgresFDW(char *serverName);
+static void ErrorIfOptionListHasNoTableName(List *optionList);
 
 
 /*
@@ -662,6 +665,29 @@ ProcessUtilityInternal(PlannedStmt *pstmt,
 		PostprocessCreateTableStmt(createStatement, queryString);
 	}
 
+	if (IsA(parsetree, CreateForeignTableStmt))
+	{
+		CreateForeignTableStmt *createForeignTableStmt =
+			(CreateForeignTableStmt *) parsetree;
+
+		CreateStmt *createTableStmt = (CreateStmt *) (&createForeignTableStmt->base);
+
+		/*
+		 * Error out with a hint if the foreign table is using postgres_fdw and
+		 * the option table_name is not provided.
+		 * Citus relays all the Citus local foreign table logic to the placement of the
+		 * Citus local table. If table_name is NOT provided, Citus would try to talk to
+		 * the foreign postgres table over the shard's table name, which would not exist
+		 * on the remote server.
+		 */
+		if (ServerUsesPostgresFDW(createForeignTableStmt->servername))
+		{
+			ErrorIfOptionListHasNoTableName(createForeignTableStmt->options);
+		}
+
+		PostprocessCreateTableStmt(createTableStmt, queryString);
+	}
+
 	/* after local command has completed, finish by executing worker DDLJobs, if any */
 	if (ddlJobs != NIL)
 	{
@@ -891,14 +917,24 @@ ShouldCheckUndistributeCitusLocalTables(void)
 static bool
 ShouldAddNewTableToMetadata(Node *parsetree)
 {
-	if (!IsA(parsetree, CreateStmt))
+	CreateStmt *createTableStmt;
+
+	if (IsA(parsetree, CreateStmt))
+	{
+		createTableStmt = (CreateStmt *) parsetree;
+	}
+	else if (IsA(parsetree, CreateForeignTableStmt))
+	{
+		CreateForeignTableStmt *createForeignTableStmt =
+			(CreateForeignTableStmt *) parsetree;
+		createTableStmt = (CreateStmt *) &(createForeignTableStmt->base);
+	}
+	else
 	{
-		/* if the command is not CREATE TABLE, we can early return false */
+		/* if the command is not CREATE [FOREIGN] TABLE, we can early return false */
 		return false;
 	}
 
-	CreateStmt *createTableStmt = (CreateStmt *) parsetree;
-
 	if (createTableStmt->relation->relpersistence == RELPERSISTENCE_TEMP ||
 		createTableStmt->partbound != NULL)
 	{
@@ -924,6 +960,50 @@ ShouldAddNewTableToMetadata(Node *parsetree)
 }
 
 
+/*
+ * ServerUsesPostgresFDW gets a foreign server name and returns true if the FDW that
+ * the server depends on is postgres_fdw. Returns false otherwise.
+ */
+static bool
+ServerUsesPostgresFDW(char *serverName)
+{
+	ForeignServer *server = GetForeignServerByName(serverName, false);
+	ForeignDataWrapper *fdw = GetForeignDataWrapper(server->fdwid);
+
+	if (strcmp(fdw->fdwname, "postgres_fdw") == 0)
+	{
+		return true;
+	}
+
+	return false;
+}
+
+
+/*
+ * ErrorIfOptionListHasNoTableName gets an option list (DefElem) and errors out
+ * if the list does not contain a table_name element.
+ */
+static void
+ErrorIfOptionListHasNoTableName(List *optionList)
+{
+	char *table_nameString = "table_name";
+	DefElem *option = NULL;
+	foreach_ptr(option, optionList)
+	{
+		char *optionName = option->defname;
+		if (strcmp(optionName, table_nameString) == 0)
+		{
+			return;
+		}
+	}
+
+	ereport(ERROR, (errmsg(
+						"table_name option must be provided when using postgres_fdw with Citus"),
+					errhint("Provide the option \"table_name\" with value target table's"
+							" name")));
+}
+
+
 /*
  * NotifyUtilityHookConstraintDropped sets ConstraintDropped to true to tell us
  * last command dropped a table constraint.

src/backend/distributed/deparser/deparse_table_stmts.c

@@ -30,7 +30,7 @@ DeparseAlterTableSchemaStmt(Node *node)
 	StringInfoData str = { 0 };
 	initStringInfo(&str);
 
-	Assert(stmt->objectType == OBJECT_TABLE);
+	Assert(stmt->objectType == OBJECT_TABLE || stmt->objectType == OBJECT_FOREIGN_TABLE);
 
 	AppendAlterTableSchemaStmt(&str, stmt);
 	return str.data;
@@ -40,8 +40,10 @@ DeparseAlterTableSchemaStmt(Node *node)
 static void
 AppendAlterTableSchemaStmt(StringInfo buf, AlterObjectSchemaStmt *stmt)
 {
-	Assert(stmt->objectType == OBJECT_TABLE);
-	appendStringInfo(buf, "ALTER TABLE ");
+	Assert(stmt->objectType == OBJECT_TABLE || stmt->objectType == OBJECT_FOREIGN_TABLE);
+
+	bool isForeignTable = stmt->objectType == OBJECT_FOREIGN_TABLE;
+	appendStringInfo(buf, "ALTER %sTABLE ", isForeignTable ? "FOREIGN " : "");
 	if (stmt->missing_ok)
 	{
 		appendStringInfo(buf, "IF EXISTS ");

src/backend/distributed/deparser/qualify_table_stmt.c

@@ -29,7 +29,7 @@ void
 QualifyAlterTableSchemaStmt(Node *node)
 {
 	AlterObjectSchemaStmt *stmt = castNode(AlterObjectSchemaStmt, node);
-	Assert(stmt->objectType == OBJECT_TABLE);
+	Assert(stmt->objectType == OBJECT_TABLE || stmt->objectType == OBJECT_FOREIGN_TABLE);
 
 	if (stmt->relation->schemaname == NULL)
 	{

src/backend/distributed/metadata/metadata_sync.c

@@ -679,21 +679,24 @@ MetadataCreateCommands(void)
 	/* after all tables are created, create the metadata */
 	foreach_ptr(cacheEntry, propagatedTableList)
 	{
-		Oid clusteredTableId = cacheEntry->relationId;
+		Oid relationId = cacheEntry->relationId;
 
 		/* add the table metadata command first*/
 		char *metadataCommand = DistributionCreateCommand(cacheEntry);
 		metadataSnapshotCommandList = lappend(metadataSnapshotCommandList,
 											  metadataCommand);
 
-		/* add the truncate trigger command after the table became distributed */
-		char *truncateTriggerCreateCommand =
-			TruncateTriggerCreateCommand(cacheEntry->relationId);
-		metadataSnapshotCommandList = lappend(metadataSnapshotCommandList,
-											  truncateTriggerCreateCommand);
+		if (!IsForeignTable(relationId))
+		{
+			/* add the truncate trigger command after the table became distributed */
+			char *truncateTriggerCreateCommand =
+				TruncateTriggerCreateCommand(cacheEntry->relationId);
+			metadataSnapshotCommandList = lappend(metadataSnapshotCommandList,
+												  truncateTriggerCreateCommand);
+		}
 
 		/* add the pg_dist_shard{,placement} entries */
-		List *shardIntervalList = LoadShardIntervalList(clusteredTableId);
+		List *shardIntervalList = LoadShardIntervalList(relationId);
 		List *shardCreateCommandList = ShardListInsertCommand(shardIntervalList);
 
 		metadataSnapshotCommandList = list_concat(metadataSnapshotCommandList,
@@ -844,8 +847,11 @@ GetDistributedTableDDLEvents(Oid relationId)
 	commandList = lappend(commandList, metadataCommand);
 
 	/* commands to create the truncate trigger of the table */
-	char *truncateTriggerCreateCommand = TruncateTriggerCreateCommand(relationId);
-	commandList = lappend(commandList, truncateTriggerCreateCommand);
+	if (!IsForeignTable(relationId))
+	{
+		char *truncateTriggerCreateCommand = TruncateTriggerCreateCommand(relationId);
+		commandList = lappend(commandList, truncateTriggerCreateCommand);
+	}
 
 	/* commands to insert pg_dist_shard & pg_dist_placement entries */
 	List *shardIntervalList = LoadShardIntervalList(relationId);

src/backend/distributed/metadata/metadata_utility.c

@@ -2162,3 +2162,14 @@ TableOwner(Oid relationId)
 
 	return GetUserNameFromId(userId, false);
 }
+
+
+/*
+ * IsForeignTable takes a relation id and returns true if it's a foreign table.
+ * Returns false otherwise.
+ */
+bool
+IsForeignTable(Oid relationId)
+{
+	return get_rel_relkind(relationId) == RELKIND_FOREIGN_TABLE;
+}

src/backend/distributed/operations/node_protocol.c

@@ -576,22 +576,6 @@ GetPreLoadTableCreationCommands(Oid relationId,
 
 	PushOverrideEmptySearchPath(CurrentMemoryContext);
 
-	/* if foreign table, fetch extension and server definitions */
-	char tableType = get_rel_relkind(relationId);
-	if (tableType == RELKIND_FOREIGN_TABLE)
-	{
-		char *extensionDef = pg_get_extensiondef_string(relationId);
-		char *serverDef = pg_get_serverdef_string(relationId);
-
-		if (extensionDef != NULL)
-		{
-			tableDDLEventList = lappend(tableDDLEventList,
-										makeTableDDLCommandString(extensionDef));
-		}
-		tableDDLEventList = lappend(tableDDLEventList,
-									makeTableDDLCommandString(serverDef));
-	}
-
 	/* fetch table schema and column option definitions */
 	char *tableSchemaDef = pg_get_tableschemadef_string(relationId,
 														includeSequenceDefaults,