Rename FindRouterWorkerList to CreateTaskPlacementListForShardIntervals

src/backend/distributed/executor/citus_custom_scan.c

@@ -545,7 +545,8 @@ RegenerateTaskForFasthPathQuery(Job *workerJob)
 	bool hasLocalRelation = false;
 
 	List *placementList =
-		FindRouterWorkerList(shardIntervalList, shardsPresent, true, hasLocalRelation);
+		CreateTaskPlacementListForShardIntervals(shardIntervalList, shardsPresent, true,
+												 hasLocalRelation);
 	uint64 shardId = INVALID_SHARD_ID;
 
 	if (shardsPresent)

src/backend/distributed/planner/multi_router_planner.c

@@ -2138,11 +2138,12 @@ PlanRouterQuery(Query *originalQuery,
 
 	bool hasLocalRelation = relationRestrictionContext->hasLocalRelation;
 
-	List *workerList =
+	List *taskPlacementList =
-		FindRouterWorkerList(*prunedShardIntervalListList, shardsPresent,
+		CreateTaskPlacementListForShardIntervals(*prunedShardIntervalListList,
-							 replacePrunedQueryWithDummy, hasLocalRelation);
+												 shardsPresent,
-
+												 replacePrunedQueryWithDummy,
-	if (workerList == NIL)
+												 hasLocalRelation);
+	if (taskPlacementList == NIL)
 	{
 		ereport(DEBUG2, (errmsg("Found no worker with all shard placements")));
 
@@ -2162,28 +2163,43 @@ PlanRouterQuery(Query *originalQuery,
 	}
 
 	*multiShardModifyQuery = false;
-	*placementList = workerList;
+	*placementList = taskPlacementList;
 	*anchorShardId = shardId;
 
 	return planningError;
 }
 
 
+/*
+ * CreateTaskPlacementListForShardIntervals returns a list of shard placements
+ * on which it can access all shards in shardIntervalListList, which contains
+ * a list of shards for each relation in the query.
+ *
+ * If the query contains a local table then hasLocalRelation should be set to
+ * true. In that case, CreateTaskPlacementListForShardIntervals only returns
+ * a placement for the local node or an empty list if the shards cannot be
+ * accessed locally.
+ *
+ * If generateDummyPlacement is true and there are no shards that need to be
+ * accessed to answer the query (shardsPresent is false), then as single
+ * placement is returned that is either local or follows a round-robin policy.
+ * A typical example is a router query that only reads an intermediate result.
+ * This will happen on the coordinator, unless the user wants to balance the
+ * load by setting the citus.task_assignment_policy.
+ */
 List *
-FindRouterWorkerList(List *shardIntervalList, bool shardsPresent,
+CreateTaskPlacementListForShardIntervals(List *shardIntervalListList, bool shardsPresent,
-					 bool replacePrunedQueryWithDummy, bool hasLocalRelation)
+										 bool generateDummyPlacement,
+										 bool hasLocalRelation)
 {
 	List *placementList = NIL;
 
-	/*
-	 * Determine the worker that has all shard placements if a shard placement found.
-	 * If no shard placement exists and replacePrunedQueryWithDummy flag is set, we will
-	 * still run the query but the result will be empty. We create a dummy shard
-	 * placement for the first active worker.
-	 */
 	if (shardsPresent)
 	{
-		List *workerList = WorkersContainingAllShards(shardIntervalList);
+		/*
+		 * Determine the workers that have all shard placements, if any.
+		 */
+		List *workerList = WorkersContainingAllShards(shardIntervalListList);
 
 		if (hasLocalRelation)
 		{
@@ -2207,7 +2223,7 @@ FindRouterWorkerList(List *shardIntervalList, bool shardsPresent,
 			placementList = workerList;
 		}
 	}
-	else if (replacePrunedQueryWithDummy)
+	else if (generateDummyPlacement)
 	{
 		ShardPlacement *dummyPlacement = CreateDummyPlacement(hasLocalRelation);
 

src/include/distributed/multi_router_planner.h

@@ -45,8 +45,9 @@ extern DeferredErrorMessage * PlanRouterQuery(Query *originalQuery,
 											  Const **partitionValueConst);
 extern List * RelationShardListForShardIntervalList(List *shardIntervalList,
 													bool *shardsPresent);
-extern List * FindRouterWorkerList(List *shardIntervalList, bool shardsPresent,
+extern List * CreateTaskPlacementListForShardIntervals(List *shardIntervalList,
-								   bool replacePrunedQueryWithDummy,
+													   bool shardsPresent,
+													   bool generateDummyPlacement,
 													   bool hasLocalRelation);
 extern List * RouterInsertTaskList(Query *query, bool parametersInQueryResolved,
 								   DeferredErrorMessage **planningError);
@@ -75,7 +76,6 @@ extern bool IsMultiRowInsert(Query *query);
 extern void AddShardIntervalRestrictionToSelect(Query *subqery,
 												ShardInterval *shardInterval);
 extern bool UpdateOrDeleteQuery(Query *query);
-extern List * WorkersContainingAllShards(List *prunedShardIntervalsList);
 
 extern uint64 GetAnchorShardId(List *relationShardList);
 extern List * TargetShardIntervalForFastPathQuery(Query *query,