implement DropTaskList before introducing local DROP table execution (#3603)

src/backend/distributed/master/master_delete_protocol.c

@@ -27,7 +27,9 @@
 #include "commands/dbcommands.h"
 #include "distributed/commands/utility_hook.h"
 #include "distributed/connection_management.h"
+#include "distributed/deparse_shard_query.h"
 #include "distributed/listutils.h"
+#include "distributed/local_executor.h"
 #include "distributed/master_protocol.h"
 #include "distributed/metadata_sync.h"
 #include "distributed/multi_client_executor.h"
@@ -78,12 +80,14 @@ static List * ShardsMatchingDeleteCriteria(Oid relationId, List *shardList,
 										   Node *deleteCriteria);
 static int DropShards(Oid relationId, char *schemaName, char *relationName,
 					  List *deletableShardIntervalList);
+static List * DropTaskList(Oid relationId, char *schemaName, char *relationName,
+						   List *deletableShardIntervalList);
 static void ExecuteDropShardPlacementCommandRemotely(ShardPlacement *shardPlacement,
 													 const char *shardRelationName,
 													 const char *dropShardPlacementCommand);
 static char * CreateDropShardPlacementCommand(const char *schemaName,
-											  const char *shardRelationName, char
+											  const char *shardRelationName,
-											  storageType);
+											  char storageType);
 
 
 /* exports for SQL callable functions */
@@ -372,6 +376,15 @@ DropShards(Oid relationId, char *schemaName, char *relationName,
 
 	UseCoordinatedTransaction();
 
+	/*
+	 * We will use below variable accross this function to decide if we can
+	 * use local execution
+	 */
+	int32 localGroupId = GetLocalGroupId();
+
+	/* DROP table commands are currently only supported from the coordinator */
+	Assert(localGroupId == COORDINATOR_GROUP_ID);
+
 	/*
 	 * At this point we intentionally decided to not use 2PC for reference
 	 * tables
@@ -381,50 +394,43 @@ DropShards(Oid relationId, char *schemaName, char *relationName,
 		CoordinatedTransactionUse2PC();
 	}
 
-	ShardInterval *shardInterval = NULL;
+	List *dropTaskList = DropTaskList(relationId, schemaName, relationName,
-	foreach_ptr(shardInterval, deletableShardIntervalList)
+									  deletableShardIntervalList);
+
+	Task *task = NULL;
+	foreach_ptr(task, dropTaskList)
 	{
-		uint64 shardId = shardInterval->shardId;
+		uint64 shardId = task->anchorShardId;
-		char *shardRelationName = pstrdup(relationName);
-
-		Assert(shardInterval->relationId == relationId);
-
-		/* build shard relation name */
-		AppendShardIdToName(&shardRelationName, shardId);
-
-		List *shardPlacementList = ShardPlacementList(shardId);
 
 		ShardPlacement *shardPlacement = NULL;
-		foreach_ptr(shardPlacement, shardPlacementList)
+		foreach_ptr(shardPlacement, task->taskPlacementList)
 		{
 			uint64 shardPlacementId = shardPlacement->placementId;
+			int32 shardPlacementGroupId = shardPlacement->groupId;
 
-			if (shardPlacement->groupId == COORDINATOR_GROUP_ID &&
+			bool isLocalShardPlacement = (shardPlacementGroupId == localGroupId);
-				IsCoordinator() &&
+
-				DropSchemaOrDBInProgress())
+			if (isLocalShardPlacement && DropSchemaOrDBInProgress() &&
+				localGroupId == COORDINATOR_GROUP_ID)
 			{
 				/*
 				 * The active DROP SCHEMA/DATABASE ... CASCADE will drop the
 				 * shard, if we try to drop it over another connection, we will
-				 * get into a distributed deadlock.
+				 * get into a distributed deadlock. Hence, just delete the shard
+				 * placement metadata and skip it for now.
 				 */
+				DeleteShardPlacementRow(shardPlacementId);
+				continue;
 			}
-			else
-			{
-				char storageType = shardInterval->storageType;
 
-				const char *dropShardPlacementCommand =
+			const char *dropShardPlacementCommand = TaskQueryString(task);
-					CreateDropShardPlacementCommand(schemaName, shardRelationName,
-													storageType);
-
-				/*
-				 * Try to open a new connection (or use an existing one) to
-				 * connect to target node to drop shard placement over that
-				 * remote connection
-				 */
 			ExecuteDropShardPlacementCommandRemotely(shardPlacement,
-														 shardRelationName,
+													 relationName,
 													 dropShardPlacementCommand);
+
+			if (isLocalShardPlacement)
+			{
+				TransactionConnectedToLocalGroup = true;
 			}
 
 			DeleteShardPlacementRow(shardPlacementId);
@@ -443,17 +449,67 @@ DropShards(Oid relationId, char *schemaName, char *relationName,
 }
 
 
+/*
+ * DropTaskList returns a list of tasks to execute a DROP command on shard
+ * placements of distributed table. This is handled separately from other
+ * DDL commands because we handle it via the DROP trigger, which is called
+ * whenever a drop cascades.
+ */
+static List *
+DropTaskList(Oid relationId, char *schemaName, char *relationName,
+			 List *deletableShardIntervalList)
+{
+	/* resulting task list */
+	List *taskList = NIL;
+
+	/* enumerate the tasks when putting them to the taskList */
+	int taskId = 1;
+
+	ShardInterval *shardInterval = NULL;
+	foreach_ptr(shardInterval, deletableShardIntervalList)
+	{
+		Assert(shardInterval->relationId == relationId);
+
+		uint64 shardId = shardInterval->shardId;
+		char storageType = shardInterval->storageType;
+
+		char *shardRelationName = pstrdup(relationName);
+
+		/* build shard relation name */
+		AppendShardIdToName(&shardRelationName, shardId);
+
+		char *dropShardPlacementCommand =
+			CreateDropShardPlacementCommand(schemaName, shardRelationName,
+											storageType);
+
+		Task *task = CitusMakeNode(Task);
+		task->jobId = INVALID_JOB_ID;
+		task->taskId = taskId++;
+		task->taskType = DDL_TASK;
+		SetTaskQueryString(task, dropShardPlacementCommand);
+		task->dependentTaskList = NULL;
+		task->replicationModel = REPLICATION_MODEL_INVALID;
+		task->anchorShardId = shardId;
+		task->taskPlacementList = ShardPlacementList(shardId);
+
+		taskList = lappend(taskList, task);
+	}
+
+	return taskList;
+}
+
+
 /*
  * ExecuteDropShardPlacementCommandRemotely executes the given DROP shard command
  * via remote critical connection.
  */
 static void
 ExecuteDropShardPlacementCommandRemotely(ShardPlacement *shardPlacement,
-										 const char *shardRelationName,
+										 const char *relationName,
 										 const char *dropShardPlacementCommand)
 {
 	Assert(shardPlacement != NULL);
-	Assert(shardRelationName != NULL);
+	Assert(relationName != NULL);
 	Assert(dropShardPlacementCommand != NULL);
 
 	uint32 connectionFlags = FOR_DDL;
@@ -470,6 +526,12 @@ ExecuteDropShardPlacementCommandRemotely(ShardPlacement *shardPlacement,
 		char *workerName = shardPlacement->nodeName;
 		uint32 workerPort = shardPlacement->nodePort;
 
+		/* build shard relation name */
+		uint64 shardId = shardPlacement->shardId;
+		char *shardRelationName = pstrdup(relationName);
+
+		AppendShardIdToName(&shardRelationName, shardId);
+
 		ereport(WARNING, (errmsg("could not connect to shard \"%s\" on node "
 								 "\"%s:%u\"", shardRelationName, workerName,
 								 workerPort),