Implement cluster_remove_node sans error handling

src/backend/distributed/citus--5.2-1--5.2-2.sql

@@ -45,7 +45,7 @@ COMMENT ON FUNCTION cluster_add_node(nodename text,
 	IS 'add node to the cluster';
 
 CREATE FUNCTION cluster_remove_node(nodename text, nodeport integer)
-	RETURNS record
+	RETURNS void
 	LANGUAGE C STRICT
 	AS 'MODULE_PATHNAME', $$cluster_remove_node$$;
 COMMENT ON FUNCTION cluster_remove_node(nodename text, nodeport integer)

src/backend/distributed/utils/metadata_cache.c

@@ -1455,6 +1455,49 @@ InsertNodeRow(int nodeid, char *nodeName, int32 nodePort, uint32 groupId)
 }
 
 
+/*
+ * DeleteNodeRow removes the requested row if it exists
+ */
+void
+DeleteNodeRow(char *nodeName, int32 nodePort)
+{
+	const int scanKeyCount = 2;
+	bool indexOK = false;
+
+	HeapTuple heapTuple = NULL;
+	SysScanDesc heapScan;
+	ScanKeyData scanKey[scanKeyCount];
+
+	Relation pgDistNode = heap_open(DistNodeRelationId(), AccessExclusiveLock);
+
+	ScanKeyInit(&scanKey[0], Anum_pg_dist_node_nodename,
+				BTEqualStrategyNumber, F_TEXTEQ, CStringGetTextDatum(nodeName));
+	ScanKeyInit(&scanKey[1], Anum_pg_dist_node_nodeport,
+				BTEqualStrategyNumber, F_INT8EQ, Int32GetDatum(nodePort));
+
+	heapScan = systable_beginscan(pgDistNode, InvalidOid, indexOK,
+								  NULL, scanKeyCount, scanKey);
+
+	heapTuple = systable_getnext(heapScan);
+	if (!HeapTupleIsValid(heapTuple))
+	{
+		ereport(ERROR, (errmsg("could not find valid entry for node \"%s:%d\"",
+							   nodeName, nodePort)));
+	}
+
+	simple_heap_delete(pgDistNode, &(heapTuple->t_self));
+
+	systable_endscan(heapScan);
+	heap_close(pgDistNode, AccessExclusiveLock);
+
+	/* ensure future commands don't use the node we just removed */
+	CitusInvalidateRelcacheByRelid(DistNodeRelationId());
+
+	/* increment the counter so that next command won't see the row */
+	CommandCounterIncrement();
+}
+
+
 /*
  * TupleToWorkerNode takes in a heap tuple from pg_dist_node, and
  * converts this tuple to an equivalent struct in memory. The function assumes

src/backend/distributed/utils/node_metadata.c

@@ -27,7 +27,6 @@
 #include "distributed/metadata_cache.h"
 #include "distributed/pg_dist_node.h"
 #include "distributed/worker_manager.h"
-#include "distributed/worker_transaction.h"
 #include "lib/stringinfo.h"
 #include "storage/lock.h"
 #include "storage/fd.h"
@@ -131,6 +130,15 @@ cluster_remove_node(PG_FUNCTION_ARGS)
 {
 	text *nodeName = PG_GETARG_TEXT_P(0);
 	int32 nodePort = PG_GETARG_INT32(1);
+	char *nodeNameString = text_to_cstring(nodeName);
+
+	DeleteNodeRow(nodeNameString, nodePort);
+
+	/*
+	 * 1) lookup the node
+	 * 2) ensure there are no existing shard placements for this node
+	 * 3) remove the row
+	 */
 
 	PG_RETURN_VOID();
 }

src/include/distributed/metadata_cache.h

@@ -54,6 +54,7 @@ extern bool IsDistributedTable(Oid relationId);
 extern ShardInterval * LoadShardInterval(uint64 shardId);
 extern DistTableCacheEntry * DistributedTableCacheEntry(Oid distributedRelationId);
 extern void InsertNodeRow(int nodeid, char *nodename, int32 nodeport, uint32 groupId);
+extern void DeleteNodeRow(char *nodename, int32 nodeport);
 extern void CitusInvalidateRelcacheByRelid(Oid relationId);
 extern void CitusInvalidateNodeCache(void);