Merge pull request #391 from citusdata/feature/rely-less-on-remote-task-check-interval

Prototype: Rely less on remote_task_check_interval.

cr: @jasonmp85

src/backend/distributed/executor/multi_client_executor.c

@@ -21,6 +21,7 @@
 #include "distributed/metadata_cache.h"
 #include "distributed/connection_cache.h"
 #include "distributed/multi_client_executor.h"
+#include "distributed/multi_server_executor.h"
 
 #include <errno.h>
 #include <unistd.h>
@@ -226,9 +227,12 @@ MultiClientConnectPoll(int32 connectionId)
 		if (readReady)
 		{
 			ClientPollingStatusArray[connectionId] = PQconnectPoll(connection);
+			connectStatus = CLIENT_CONNECTION_BUSY;
+		}
+		else
+		{
+			connectStatus = CLIENT_CONNECTION_BUSY_READ;
 		}
-
-		connectStatus = CLIENT_CONNECTION_BUSY;
 	}
 	else if (pollingStatus == PGRES_POLLING_WRITING)
 	{
@@ -236,9 +240,12 @@ MultiClientConnectPoll(int32 connectionId)
 		if (writeReady)
 		{
 			ClientPollingStatusArray[connectionId] = PQconnectPoll(connection);
+			connectStatus = CLIENT_CONNECTION_BUSY;
+		}
+		else
+		{
+			connectStatus = CLIENT_CONNECTION_BUSY_WRITE;
 		}
-
-		connectStatus = CLIENT_CONNECTION_BUSY;
 	}
 	else if (pollingStatus == PGRES_POLLING_FAILED)
 	{
@@ -691,6 +698,160 @@ MultiClientCopyData(int32 connectionId, int32 fileDescriptor)
 }
 
 
+/*
+ * MultiClientCreateWaitInfo creates a WaitInfo structure, capable of keeping
+ * track of what maxConnections connections are waiting for; to allow
+ * efficiently waiting for all of them at once.
+ *
+ * Connections can be added using MultiClientRegisterWait(). All added
+ * connections can then be waited upon together using MultiClientWait().
+ */
+WaitInfo *
+MultiClientCreateWaitInfo(int maxConnections)
+{
+	WaitInfo *waitInfo = palloc(sizeof(WaitInfo));
+
+	waitInfo->maxWaiters = maxConnections;
+	waitInfo->pollfds = palloc(maxConnections * sizeof(struct pollfd));
+
+	/* initialize remaining fields */
+	MultiClientResetWaitInfo(waitInfo);
+
+	return waitInfo;
+}
+
+
+/* MultiClientResetWaitInfo clears all pending waits from a WaitInfo. */
+void
+MultiClientResetWaitInfo(WaitInfo *waitInfo)
+{
+	waitInfo->registeredWaiters = 0;
+	waitInfo->haveReadyWaiter = false;
+	waitInfo->haveFailedWaiter = false;
+}
+
+
+/* MultiClientFreeWaitInfo frees a resources associated with a waitInfo struct. */
+void
+MultiClientFreeWaitInfo(WaitInfo *waitInfo)
+{
+	pfree(waitInfo->pollfds);
+	pfree(waitInfo);
+}
+
+
+/*
+ * MultiClientRegisterWait adds a connection to be waited upon, waiting for
+ * executionStatus.
+ */
+void
+MultiClientRegisterWait(WaitInfo *waitInfo, TaskExecutionStatus executionStatus,
+						int32 connectionId)
+{
+	PGconn *connection = NULL;
+	struct pollfd *pollfd = NULL;
+
+	Assert(waitInfo->registeredWaiters < waitInfo->maxWaiters);
+
+	if (executionStatus == TASK_STATUS_READY)
+	{
+		waitInfo->haveReadyWaiter = true;
+		return;
+	}
+	else if (executionStatus == TASK_STATUS_ERROR)
+	{
+		waitInfo->haveFailedWaiter = true;
+		return;
+	}
+
+	connection = ClientConnectionArray[connectionId];
+	pollfd = &waitInfo->pollfds[waitInfo->registeredWaiters];
+	pollfd->fd = PQsocket(connection);
+	if (executionStatus == TASK_STATUS_SOCKET_READ)
+	{
+		pollfd->events = POLLERR | POLLIN;
+	}
+	else if (executionStatus == TASK_STATUS_SOCKET_WRITE)
+	{
+		pollfd->events = POLLERR | POLLOUT;
+	}
+	waitInfo->registeredWaiters++;
+}
+
+
+/*
+ * MultiClientWait waits until at least one connection added with
+ * MultiClientRegisterWait is ready to be processed again.
+ */
+void
+MultiClientWait(WaitInfo *waitInfo)
+{
+	long sleepIntervalPerCycle = RemoteTaskCheckInterval * 1000L;
+
+	/*
+	 * If we had a failure, we always want to sleep for a bit, to prevent
+	 * flooding the other system, probably making the situation worse.
+	 */
+	if (waitInfo->haveFailedWaiter)
+	{
+		pg_usleep(sleepIntervalPerCycle);
+		return;
+	}
+
+	/* if there are tasks that already need attention again, don't wait */
+	if (waitInfo->haveReadyWaiter)
+	{
+		return;
+	}
+
+	while (true)
+	{
+		/*
+		 * Wait for activity on any of the sockets. Limit the maximum time
+		 * spent waiting in one wait cycle, as insurance against edge
+		 * cases. For efficiency we don't want wake up quite as often as
+		 * citus.remote_task_check_interval, so rather arbitrarily sleep ten
+		 * times as long.
+		 */
+		int rc = poll(waitInfo->pollfds, waitInfo->registeredWaiters,
+					  sleepIntervalPerCycle * 10);
+
+		if (rc < 0)
+		{
+			/*
+			 * Signals that arrive can interrupt our poll(). In that case just
+			 * check for interrupts, and try again. Every other error is
+			 * unexpected and treated as such.
+			 */
+			if (errno == EAGAIN || errno == EINTR)
+			{
+				CHECK_FOR_INTERRUPTS();
+
+				/* maximum wait starts at max again, but that's ok, it's just a stopgap */
+				continue;
+			}
+			else
+			{
+				ereport(ERROR, (errcode_for_file_access(),
+								errmsg("poll failed: %m")));
+			}
+		}
+		else if (rc == 0)
+		{
+			ereport(DEBUG2,
+					(errmsg("waiting for activity on tasks took longer than %ld ms",
+							(long) RemoteTaskCheckInterval * 10)));
+		}
+
+		/*
+		 * At least one fd changed received a readiness notification, time to
+		 * process tasks again.
+		 */
+		return;
+	}
+}
+
+
 /*
  * ClearRemainingResults reads result objects from the connection until we get
  * null, and clears these results. This is the last step in completing an async

src/backend/distributed/executor/multi_real_time_executor.c

@@ -21,6 +21,7 @@
 
 #include <sys/stat.h>
 #include <unistd.h>
+#include <poll.h>
 
 #include "commands/dbcommands.h"
 #include "distributed/multi_client_executor.h"
@@ -28,10 +29,12 @@
 #include "distributed/multi_server_executor.h"
 #include "distributed/worker_protocol.h"
 #include "storage/fd.h"
+#include "utils/timestamp.h"
 
 
 /* Local functions forward declarations */
-static ConnectAction ManageTaskExecution(Task *task, TaskExecution *taskExecution);
+static ConnectAction ManageTaskExecution(Task *task, TaskExecution *taskExecution,
+										 TaskExecutionStatus *executionStatus);
 static bool TaskExecutionReadyToStart(TaskExecution *taskExecution);
 static bool TaskExecutionCompleted(TaskExecution *taskExecution);
 static void CancelTaskExecutionIfActive(TaskExecution *taskExecution);
@@ -76,6 +79,7 @@ MultiRealTimeExecute(Job *job)
 	List *workerNodeList = NIL;
 	HTAB *workerHash = NULL;
 	const char *workerHashName = "Worker node hash";
+	WaitInfo *waitInfo = MultiClientCreateWaitInfo(list_length(taskList));
 
 	workerNodeList = WorkerNodeList();
 	workerHash = WorkerHash(workerHashName, workerNodeList);
@@ -99,12 +103,15 @@ MultiRealTimeExecute(Job *job)
 		ListCell *taskCell = NULL;
 		ListCell *taskExecutionCell = NULL;
 
+		MultiClientResetWaitInfo(waitInfo);
+
 		forboth(taskCell, taskList, taskExecutionCell, taskExecutionList)
 		{
 			Task *task = (Task *) lfirst(taskCell);
 			TaskExecution *taskExecution = (TaskExecution *) lfirst(taskExecutionCell);
 			ConnectAction connectAction = CONNECT_ACTION_NONE;
 			WorkerNodeState *workerNodeState = NULL;
+			TaskExecutionStatus executionStatus;
 
 			workerNodeState = LookupWorkerForTask(workerHash, task, taskExecution);
 
@@ -117,7 +124,7 @@ MultiRealTimeExecute(Job *job)
 			}
 
 			/* call the function that performs the core task execution logic */
-			connectAction = ManageTaskExecution(task, taskExecution);
+			connectAction = ManageTaskExecution(task, taskExecution, &executionStatus);
 
 			/* update the connection counter for throttling */
 			UpdateConnectionCounter(workerNodeState, connectAction);
@@ -139,20 +146,38 @@ MultiRealTimeExecute(Job *job)
 			{
 				completedTaskCount++;
 			}
+			else
+			{
+				uint32 currentIndex = taskExecution->currentNodeIndex;
+				int32 *connectionIdArray = taskExecution->connectionIdArray;
+				int32 connectionId = connectionIdArray[currentIndex];
+
+				/*
+				 * If not done with the task yet, make note of what this task
+				 * and its associated connection is waiting for.
+				 */
+				MultiClientRegisterWait(waitInfo, executionStatus, connectionId);
+			}
 		}
 
-		/* check if all tasks completed; otherwise sleep to avoid tight loop */
+		/*
+		 * Check if all tasks completed; otherwise wait as appropriate to
+		 * avoid a tight loop. That means we immediately continue if tasks are
+		 * ready to be processed further, and block when we're waiting for
+		 * network IO.
+		 */
 		if (completedTaskCount == taskCount)
 		{
 			allTasksCompleted = true;
 		}
 		else
 		{
-			long sleepIntervalPerCycle = RemoteTaskCheckInterval * 1000L;
-			pg_usleep(sleepIntervalPerCycle);
+			MultiClientWait(waitInfo);
 		}
 	}
 
+	MultiClientFreeWaitInfo(waitInfo);
+
 	/*
 	 * We prevent cancel/die interrupts until we clean up connections to worker
 	 * nodes. Note that for the above while loop, if the user Ctrl+C's a query
@@ -172,6 +197,9 @@ MultiRealTimeExecute(Job *job)
 	/*
 	 * If cancel might have been sent, give remote backends some time to flush
 	 * their responses. This avoids some broken pipe logs on the backend-side.
+	 *
+	 * FIXME: This shouldn't be dependant on RemoteTaskCheckInterval; they're
+	 * unrelated type of delays.
 	 */
 	if (taskFailed || QueryCancelPending)
 	{
@@ -213,10 +241,12 @@ MultiRealTimeExecute(Job *job)
  * Note that this function directly manages a task's execution by opening up a
  * separate connection to the worker node for each execution. The function
  * returns a ConnectAction enum indicating whether a connection has been opened
- * or closed in this call.
+ * or closed in this call.  Via the executionStatus parameter this function returns
+ * what a Task is blocked on.
  */
 static ConnectAction
-ManageTaskExecution(Task *task, TaskExecution *taskExecution)
+ManageTaskExecution(Task *task, TaskExecution *taskExecution,
+					TaskExecutionStatus *executionStatus)
 {
 	TaskExecStatus *taskStatusArray = taskExecution->taskStatusArray;
 	int32 *connectionIdArray = taskExecution->connectionIdArray;
@@ -229,6 +259,9 @@ ManageTaskExecution(Task *task, TaskExecution *taskExecution)
 	uint32 nodePort = taskPlacement->nodePort;
 	ConnectAction connectAction = CONNECT_ACTION_NONE;
 
+	/* as most state transitions don't require blocking, default to not waiting */
+	*executionStatus = TASK_STATUS_READY;
+
 	switch (currentStatus)
 	{
 		case EXEC_TASK_CONNECT_START:
@@ -246,12 +279,14 @@ ManageTaskExecution(Task *task, TaskExecution *taskExecution)
 			if (connectionId != INVALID_CONNECTION_ID)
 			{
 				taskStatusArray[currentIndex] = EXEC_TASK_CONNECT_POLL;
-				taskExecution->connectPollCount = 0;
+				taskExecution->connectStartTime = GetCurrentTimestamp();
 				connectAction = CONNECT_ACTION_OPENED;
 			}
 			else
 			{
+				*executionStatus = TASK_STATUS_ERROR;
 				AdjustStateForFailure(taskExecution);
+				break;
 			}
 
 			break;
@@ -273,6 +308,17 @@ ManageTaskExecution(Task *task, TaskExecution *taskExecution)
 			}
 			else if (pollStatus == CLIENT_CONNECTION_BUSY)
 			{
+				/* immediately retry */
+				taskStatusArray[currentIndex] = EXEC_TASK_CONNECT_POLL;
+			}
+			else if (pollStatus == CLIENT_CONNECTION_BUSY_READ)
+			{
+				*executionStatus = TASK_STATUS_SOCKET_READ;
+				taskStatusArray[currentIndex] = EXEC_TASK_CONNECT_POLL;
+			}
+			else if (pollStatus == CLIENT_CONNECTION_BUSY_WRITE)
+			{
+				*executionStatus = TASK_STATUS_SOCKET_WRITE;
 				taskStatusArray[currentIndex] = EXEC_TASK_CONNECT_POLL;
 			}
 			else if (pollStatus == CLIENT_CONNECTION_BAD)
@@ -281,12 +327,12 @@ ManageTaskExecution(Task *task, TaskExecution *taskExecution)
 			}
 
 			/* now check if we have been trying to connect for too long */
-			taskExecution->connectPollCount++;
-			if (pollStatus == CLIENT_CONNECTION_BUSY)
+			if (pollStatus == CLIENT_CONNECTION_BUSY_READ ||
+				pollStatus == CLIENT_CONNECTION_BUSY_WRITE)
 			{
-				uint32 maxCount = REMOTE_NODE_CONNECT_TIMEOUT / RemoteTaskCheckInterval;
-				uint32 currentCount = taskExecution->connectPollCount;
-				if (currentCount >= maxCount)
+				if (TimestampDifferenceExceeds(taskExecution->connectStartTime,
+											   GetCurrentTimestamp(),
+											   REMOTE_NODE_CONNECT_TIMEOUT))
 				{
 					ereport(WARNING, (errmsg("could not establish asynchronous "
 											 "connection after %u ms",
@@ -317,6 +363,12 @@ ManageTaskExecution(Task *task, TaskExecution *taskExecution)
 			/* try next worker node */
 			AdjustStateForFailure(taskExecution);
 
+			/*
+			 * Add a delay, to avoid potentially excerbating problems by
+			 * looping quickly
+			 */
+			*executionStatus = TASK_STATUS_ERROR;
+
 			break;
 		}
 
@@ -372,6 +424,7 @@ ManageTaskExecution(Task *task, TaskExecution *taskExecution)
 			/* check if query results are in progress or unavailable */
 			if (resultStatus == CLIENT_RESULT_BUSY)
 			{
+				*executionStatus = TASK_STATUS_SOCKET_READ;
 				taskStatusArray[currentIndex] = EXEC_FETCH_TASK_RUNNING;
 				break;
 			}
@@ -446,6 +499,7 @@ ManageTaskExecution(Task *task, TaskExecution *taskExecution)
 			if (resultStatus == CLIENT_RESULT_BUSY)
 			{
 				taskStatusArray[currentIndex] = EXEC_COMPUTE_TASK_RUNNING;
+				*executionStatus = TASK_STATUS_SOCKET_READ;
 				break;
 			}
 			else if (resultStatus == CLIENT_RESULT_UNAVAILABLE)
@@ -511,6 +565,7 @@ ManageTaskExecution(Task *task, TaskExecution *taskExecution)
 			if (copyStatus == CLIENT_COPY_MORE)
 			{
 				taskStatusArray[currentIndex] = EXEC_COMPUTE_TASK_COPYING;
+				*executionStatus = TASK_STATUS_SOCKET_READ;
 			}
 			else if (copyStatus == CLIENT_COPY_DONE)
 			{

src/backend/distributed/executor/multi_server_executor.c

@@ -226,7 +226,7 @@ InitTaskExecution(Task *task, TaskExecStatus initialTaskExecStatus)
 	taskExecution->jobId = task->jobId;
 	taskExecution->taskId = task->taskId;
 	taskExecution->nodeCount = nodeCount;
-	taskExecution->connectPollCount = 0;
+	taskExecution->connectStartTime = 0;
 	taskExecution->currentNodeIndex = 0;
 	taskExecution->dataFetchTaskIndex = -1;
 	taskExecution->failureCount = 0;

src/backend/distributed/executor/multi_task_tracker_executor.c

@@ -850,7 +850,9 @@ TrackerConnectPoll(TaskTracker *taskTracker)
 			{
 				taskTracker->trackerStatus = TRACKER_CONNECTED;
 			}
-			else if (pollStatus == CLIENT_CONNECTION_BUSY)
+			else if (pollStatus == CLIENT_CONNECTION_BUSY ||
+					 pollStatus == CLIENT_CONNECTION_BUSY_READ ||
+					 pollStatus == CLIENT_CONNECTION_BUSY_WRITE)
 			{
 				taskTracker->trackerStatus = TRACKER_CONNECT_POLL;
 			}
@@ -864,7 +866,8 @@ TrackerConnectPoll(TaskTracker *taskTracker)
 
 			/* now check if we have been trying to connect for too long */
 			taskTracker->connectPollCount++;
-			if (pollStatus == CLIENT_CONNECTION_BUSY)
+			if (pollStatus == CLIENT_CONNECTION_BUSY_READ ||
+				pollStatus == CLIENT_CONNECTION_BUSY_WRITE)
 			{
 				uint32 maxCount = REMOTE_NODE_CONNECT_TIMEOUT / RemoteTaskCheckInterval;
 				uint32 currentCount = taskTracker->connectPollCount;

src/include/distributed/multi_client_executor.h

@@ -14,7 +14,6 @@
 #ifndef MULTI_CLIENT_EXECUTOR_H
 #define MULTI_CLIENT_EXECUTOR_H
 
-
 #define INVALID_CONNECTION_ID -1  /* identifies an invalid connection */
 #define CLIENT_CONNECT_TIMEOUT 5  /* connection timeout in seconds */
 #define MAX_CONNECTION_COUNT 2048 /* simultaneous client connection count */
@@ -28,7 +27,9 @@ typedef enum
 	CLIENT_INVALID_CONNECT = 0,
 	CLIENT_CONNECTION_BAD = 1,
 	CLIENT_CONNECTION_BUSY = 2,
-	CLIENT_CONNECTION_READY = 3
+	CLIENT_CONNECTION_BUSY_READ = 3,
+	CLIENT_CONNECTION_BUSY_WRITE = 4,
+	CLIENT_CONNECTION_READY = 5
 } ConnectStatus;
 
 
@@ -72,6 +73,29 @@ typedef enum
 } BatchQueryStatus;
 
 
+/* Enumeration to track whether a task is ready to run and, if not, what it's blocked on*/
+typedef enum TaskExecutionStatus
+{
+	TASK_STATUS_INVALID = 0,
+	TASK_STATUS_ERROR, /* error occured */
+	TASK_STATUS_READY, /* task ready to be processed further */
+	TASK_STATUS_SOCKET_READ, /* waiting for connection to become ready for reads */
+	TASK_STATUS_SOCKET_WRITE /* waiting for connection to become ready for writes */
+} TaskExecutionStatus;
+
+
+struct pollfd; /* forward declared, to avoid having to include poll.h */
+
+typedef struct WaitInfo
+{
+	int maxWaiters;
+	struct pollfd *pollfds;
+	int registeredWaiters;
+	bool haveReadyWaiter;
+	bool haveFailedWaiter;
+} WaitInfo;
+
+
 /* Function declarations for executing client-side (libpq) logic. */
 extern int32 MultiClientConnect(const char *nodeName, uint32 nodePort,
 								const char *nodeDatabase, const char *nodeUser);
@@ -91,6 +115,13 @@ extern BatchQueryStatus MultiClientBatchResult(int32 connectionId, void **queryR
 											   int *rowCount, int *columnCount);
 extern char * MultiClientGetValue(void *queryResult, int rowIndex, int columnIndex);
 extern void MultiClientClearResult(void *queryResult);
+extern WaitInfo * MultiClientCreateWaitInfo(int maxConnections);
+
+extern void MultiClientResetWaitInfo(WaitInfo *waitInfo);
+extern void MultiClientFreeWaitInfo(WaitInfo *waitInfo);
+extern void MultiClientRegisterWait(WaitInfo *waitInfo, TaskExecutionStatus waitStatus,
+									int32 connectionId);
+extern void MultiClientWait(WaitInfo *waitInfo);
 
 
 #endif /* MULTI_CLIENT_EXECUTOR_H */

src/include/distributed/multi_physical_planner.h

@@ -14,6 +14,7 @@
 #ifndef MULTI_PHYSICAL_PLANNER_H
 #define MULTI_PHYSICAL_PLANNER_H
 
+#include "datatype/timestamp.h"
 #include "distributed/citus_nodes.h"
 #include "distributed/master_metadata_utility.h"
 #include "distributed/multi_logical_planner.h"

src/include/distributed/multi_server_executor.h

@@ -121,7 +121,7 @@ struct TaskExecution
 	TransmitExecStatus *transmitStatusArray;
 	int32 *connectionIdArray;
 	int32 *fileDescriptorArray;
-	uint32 connectPollCount;
+	TimestampTz connectStartTime;
 	uint32 nodeCount;
 	uint32 currentNodeIndex;
 	uint32 querySourceNodeIndex; /* only applies to map fetch tasks */