Remove dependency on placement caches from DROP

src/backend/distributed/metadata/metadata_cache.c

@@ -1054,6 +1054,61 @@ ResolveGroupShardPlacement(GroupShardPlacement *groupShardPlacement,
 }
 
 
+/*
+ * ResolveGroupShardPlacementViaCatalog takes a GroupShardPlacement and adds additional
+ * data to it, such as the node we should consider it to be on.
+ *
+ * Resides here because it shares code with ResolveGroupShardPlacement in this file.
+ * Unlike ResolveGroupShardPlacement, this method does not access cache entries for Citus
+ * tables.
+ */
+ShardPlacement *
+ResolveGroupShardPlacementViaCatalog(GroupShardPlacement *groupShardPlacement,
+									 Oid relationId,
+									 ShardInterval *shardInterval)
+{
+	ShardPlacement *shardPlacement = CitusMakeNode(ShardPlacement);
+	int32 groupId = groupShardPlacement->groupId;
+	WorkerNode *workerNode = LookupNodeForGroup(groupId);
+
+	/* copy everything into shardPlacement but preserve the header */
+	CitusNode header = shardPlacement->type;
+	GroupShardPlacement *shardPlacementAsGroupPlacement =
+		(GroupShardPlacement *) shardPlacement;
+	*shardPlacementAsGroupPlacement = *groupShardPlacement;
+	shardPlacement->type = header;
+
+	SetPlacementNodeMetadata(shardPlacement, workerNode);
+
+	/* fill in remaining fields */
+	char partitionMethod = PartitionMethodViaCatalog(relationId);
+	Assert(partitionMethod != 0);
+	shardPlacement->partitionMethod = partitionMethod;
+
+	uint32 colocationId = ColocationIdViaCatalog(relationId);
+	shardPlacement->colocationGroupId = colocationId;
+
+	if (partitionMethod == DISTRIBUTE_BY_HASH)
+	{
+		Assert(shardInterval->minValueExists);
+		Assert(shardInterval->valueTypeId == INT4OID);
+
+		/*
+		 * Use the lower boundary of the interval's range to identify
+		 * it for colocation purposes. That remains meaningful even if
+		 * a concurrent session splits a shard.
+		 */
+		shardPlacement->representativeValue = DatumGetInt32(shardInterval->minValue);
+	}
+	else
+	{
+		shardPlacement->representativeValue = 0;
+	}
+
+	return shardPlacement;
+}
+
+
 /*
  * HasAnyNodes returns whether there are any nodes in pg_dist_node.
  */
@@ -1892,7 +1947,7 @@ BuildCachedShardList(CitusTableCacheEntry *cacheEntry)
 		cacheEntry->shardIntervalArrayLength++;
 
 		/* build list of shard placements */
-		List *placementList = BuildShardPlacementList(shardId);
+		List *placementList = BuildGroupShardPlacementList(shardId);
 		int numberOfPlacements = list_length(placementList);
 
 		/* and copy that list into the cache entry */

src/backend/distributed/metadata/metadata_utility.c

@@ -1466,7 +1466,7 @@ ActiveShardPlacementListOnGroup(uint64 shardId, int32 groupId)
 
 /*
  * ActiveShardPlacementList finds shard placements for the given shardId from
- * system catalogs, chooses placements that are in active state, and returns
+ * metadata cache, chooses placements that are in active state, and returns
  * these shard placements in a new list.
  */
 List *
@@ -1545,7 +1545,7 @@ ActiveShardPlacementWorkerNode(uint64 shardId)
 
 
 /*
- * BuildShardPlacementList finds shard placements for the given shardId from
+ * BuildGroupShardPlacementList finds shard placements for the given shardId from
  * system catalogs, converts these placements to their in-memory
  * representation, and returns the converted shard placements in a new list.
  *
@@ -1553,9 +1553,9 @@ ActiveShardPlacementWorkerNode(uint64 shardId)
  * because it shares code with other routines in this file.
  */
 List *
-BuildShardPlacementList(int64 shardId)
+BuildGroupShardPlacementList(int64 shardId)
 {
-	List *shardPlacementList = NIL;
+	List *groupShardPlacementList = NIL;
 	ScanKeyData scanKey[1];
 	int scanKeyCount = 1;
 	bool indexOK = true;
@@ -1575,10 +1575,10 @@ BuildShardPlacementList(int64 shardId)
 	{
 		TupleDesc tupleDescriptor = RelationGetDescr(pgPlacement);
 
-		GroupShardPlacement *placement =
+		GroupShardPlacement *groupShardPlacement =
 			TupleToGroupShardPlacement(tupleDescriptor, heapTuple);
 
-		shardPlacementList = lappend(shardPlacementList, placement);
+		groupShardPlacementList = lappend(groupShardPlacementList, groupShardPlacement);
 
 		heapTuple = systable_getnext(scanDescriptor);
 	}
@@ -1586,12 +1586,12 @@ BuildShardPlacementList(int64 shardId)
 	systable_endscan(scanDescriptor);
 	table_close(pgPlacement, NoLock);
 
-	return shardPlacementList;
+	return groupShardPlacementList;
 }
 
 
 /*
- * BuildShardPlacementListForGroup finds shard placements for the given groupId
+ * AllShardPlacementsOnNodeGroup finds shard placements for the given groupId
  * from system catalogs, converts these placements to their in-memory
  * representation, and returns the converted shard placements in a new list.
  */

src/backend/distributed/operations/delete_protocol.c

@@ -365,6 +365,18 @@ DropTaskList(Oid relationId, char *schemaName, char *relationName,
 			CreateDropShardPlacementCommand(schemaName, shardRelationName,
 											storageType);
 
+		/* build shard placement list using catalog only */
+		List *groupShardPlacementList = BuildGroupShardPlacementList(shardId);
+		List *shardPlacementList = NIL;
+		GroupShardPlacement *groupShardPlacement = NULL;
+		foreach_ptr(groupShardPlacement, groupShardPlacementList)
+		{
+			ShardPlacement *placement =
+				ResolveGroupShardPlacementViaCatalog(groupShardPlacement, relationId,
+													 shardInterval);
+			shardPlacementList = lappend(shardPlacementList, placement);
+		}
+
 		Task *task = CitusMakeNode(Task);
 		task->jobId = INVALID_JOB_ID;
 		task->taskId = taskId++;
@@ -373,7 +385,7 @@ DropTaskList(Oid relationId, char *schemaName, char *relationName,
 		task->dependentTaskList = NULL;
 		task->replicationModel = REPLICATION_MODEL_INVALID;
 		task->anchorShardId = shardId;
-		task->taskPlacementList = ShardPlacementList(shardId);
+		task->taskPlacementList = shardPlacementList;
 
 		taskList = lappend(taskList, task);
 	}

src/include/distributed/metadata_cache.h

@@ -170,6 +170,10 @@ extern CitusTableCacheEntry * GetCitusTableCacheEntry(Oid distributedRelationId)
 extern CitusTableCacheEntry * LookupCitusTableCacheEntry(Oid relationId);
 extern DistObjectCacheEntry * LookupDistObjectCacheEntry(Oid classid, Oid objid, int32
 														 objsubid);
+extern ShardPlacement * ResolveGroupShardPlacementViaCatalog(
+	GroupShardPlacement *groupShardPlacement,
+	Oid relationId,
+	ShardInterval *shardInterval);
 extern int32 GetLocalGroupId(void);
 extern int32 GetLocalNodeId(void);
 extern void CitusTableCacheFlushInvalidatedEntries(void);

src/include/distributed/metadata_utility.h

@@ -296,7 +296,7 @@ extern List * ActiveShardPlacementList(uint64 shardId);
 extern List * ShardPlacementListSortedByWorker(uint64 shardId);
 extern ShardPlacement * ActiveShardPlacement(uint64 shardId, bool missingOk);
 extern WorkerNode * ActiveShardPlacementWorkerNode(uint64 shardId);
-extern List * BuildShardPlacementList(int64 shardId);
+extern List * BuildGroupShardPlacementList(int64 shardId);
 extern List * AllShardPlacementsOnNodeGroup(int32 groupId);
 extern List * GroupShardPlacementsForTableOnGroup(Oid relationId, int32 groupId);
 extern StringInfo GenerateSizeQueryOnMultiplePlacements(List *shardIntervalList,