EXEC_BACKEND: don't put pointers to shared hashes into shared memory

Store pointers to shared hashes in process-local variables. Previously
pointers to shared hashes were put into shared memory. This causes
problems on EXEC_BACKEND because everybody calls execve and receives a
brand new address space; the shared hash will be in a different place
for every backend. (normally we call fork, which gives you a copy of the
address space, so these pointers remain constant)

src/backend/distributed/utils/maintenanced.c

@@ -51,7 +51,7 @@ typedef struct MaintenanceDaemonControlData
 	/*
 	 * Lock protecting the shared memory state.  This is to be taken when
 	 * looking up (shared mode) or inserting (exclusive mode) per-database
-	 * data in dbHash.
+	 * data in MaintenanceDaemonDBHash.
 	 */
 	int trancheId;
 #if (PG_VERSION_NUM >= 100000)
@@ -60,12 +60,6 @@ typedef struct MaintenanceDaemonControlData
 	LWLockTranche lockTranche;
 #endif
 	LWLock lock;
-
-	/*
-	 * Hash-table of workers, one entry for each database with citus
-	 * activated.
-	 */
-	HTAB *dbHash;
 } MaintenanceDaemonControlData;
 
 
@@ -90,6 +84,12 @@ double DistributedDeadlockDetectionTimeoutFactor = 2.0;
 static shmem_startup_hook_type prev_shmem_startup_hook = NULL;
 static MaintenanceDaemonControlData *MaintenanceDaemonControl = NULL;
 
+/*
+ * Hash-table of workers, one entry for each database with citus
+ * activated.
+ */
+static HTAB *MaintenanceDaemonDBHash;
+
 static volatile sig_atomic_t got_SIGHUP = false;
 
 static void MaintenanceDaemonSigHupHandler(SIGNAL_ARGS);
@@ -128,7 +128,7 @@ InitializeMaintenanceDaemonBackend(void)
 
 	LWLockAcquire(&MaintenanceDaemonControl->lock, LW_EXCLUSIVE);
 
-	dbData = (MaintenanceDaemonDBData *) hash_search(MaintenanceDaemonControl->dbHash,
+	dbData = (MaintenanceDaemonDBData *) hash_search(MaintenanceDaemonDBHash,
 													 &MyDatabaseId,
 													 HASH_ENTER_NULL, &found);
 
@@ -225,8 +225,7 @@ CitusMaintenanceDaemonMain(Datum main_arg)
 	LWLockAcquire(&MaintenanceDaemonControl->lock, LW_SHARED);
 
 	myDbData = (MaintenanceDaemonDBData *)
-			   hash_search(MaintenanceDaemonControl->dbHash, &databaseOid,
-						   HASH_FIND, NULL);
+			   hash_search(MaintenanceDaemonDBHash, &databaseOid, HASH_FIND, NULL);
 	if (!myDbData)
 	{
 		/*
@@ -530,10 +529,9 @@ MaintenanceDaemonShmemInit(void)
 	hashInfo.hash = tag_hash;
 	hashFlags = (HASH_ELEM | HASH_FUNCTION);
 
-	MaintenanceDaemonControl->dbHash =
-		ShmemInitHash("Maintenance Database Hash",
-					  max_worker_processes, max_worker_processes,
-					  &hashInfo, hashFlags);
+	MaintenanceDaemonDBHash = ShmemInitHash("Maintenance Database Hash",
+											max_worker_processes, max_worker_processes,
+											&hashInfo, hashFlags);
 
 	LWLockRelease(AddinShmemInitLock);
 
@@ -622,7 +620,7 @@ StopMaintenanceDaemon(Oid databaseId)
 
 	LWLockAcquire(&MaintenanceDaemonControl->lock, LW_EXCLUSIVE);
 
-	dbData = (MaintenanceDaemonDBData *) hash_search(MaintenanceDaemonControl->dbHash,
+	dbData = (MaintenanceDaemonDBData *) hash_search(MaintenanceDaemonDBHash,
 													 &databaseId, HASH_REMOVE, &found);
 	if (found)
 	{

src/backend/distributed/worker/task_tracker.c

@@ -56,6 +56,9 @@ int MaxTrackedTasksPerNode = 1024; /* max number of tracked tasks */
 int MaxTaskStringSize = 12288; /* max size of a worker task call string in bytes */
 WorkerTasksSharedStateData *WorkerTasksSharedState; /* shared memory state */
 
+/* Hash table shared by the task tracker and task tracker protocol functions */
+HTAB *TaskTrackerTaskHash = NULL; /* shared memory */
+
 static shmem_startup_hook_type prev_shmem_startup_hook = NULL;
 
 /* Flags set by interrupt handlers for later service in the main loop */
@@ -246,17 +249,17 @@ TaskTrackerMain(Datum main_arg)
 			ExitOnAnyError = true;
 
 			/* Close open connections to local backends */
-			TrackerCleanupConnections(WorkerTasksSharedState->taskHash);
+			TrackerCleanupConnections(TaskTrackerTaskHash);
 
 			/* Add a sentinel task to the shared hash to mark shutdown */
-			TrackerRegisterShutDown(WorkerTasksSharedState->taskHash);
+			TrackerRegisterShutDown(TaskTrackerTaskHash);
 
 			/* Normal exit from the task tracker is here */
 			proc_exit(0);
 		}
 
 		/* Call the function that does the actual work */
-		ManageWorkerTasksHash(WorkerTasksSharedState->taskHash);
+		ManageWorkerTasksHash(TaskTrackerTaskHash);
 
 		/* Sleep for the configured time */
 		TrackerDelayLoop();
@@ -281,7 +284,7 @@ WorkerTasksHashEnter(uint64 jobId, uint32 taskId)
 	searchTask.taskId = taskId;
 
 	hashKey = (void *) &searchTask;
-	workerTask = (WorkerTask *) hash_search(WorkerTasksSharedState->taskHash, hashKey,
+	workerTask = (WorkerTask *) hash_search(TaskTrackerTaskHash, hashKey,
 											HASH_ENTER_NULL, &handleFound);
 	if (workerTask == NULL)
 	{
@@ -318,7 +321,7 @@ WorkerTasksHashFind(uint64 jobId, uint32 taskId)
 	searchTask.taskId = taskId;
 
 	hashKey = (void *) &searchTask;
-	workerTask = (WorkerTask *) hash_search(WorkerTasksSharedState->taskHash, hashKey,
+	workerTask = (WorkerTask *) hash_search(TaskTrackerTaskHash, hashKey,
 											HASH_FIND, NULL);
 
 	return workerTask;
@@ -601,14 +604,12 @@ TaskTrackerShmemInit(void)
 	}
 
 	/*  allocate hash table */
-	WorkerTasksSharedState->taskHash =
-		ShmemInitHash("Worker Task Hash",
-					  initTableSize, maxTableSize,
-					  &info, hashFlags);
+	TaskTrackerTaskHash = ShmemInitHash("Worker Task Hash", initTableSize, maxTableSize,
+										&info, hashFlags);
 
 	LWLockRelease(AddinShmemInitLock);
 
-	Assert(WorkerTasksSharedState->taskHash != NULL);
+	Assert(TaskTrackerTaskHash != NULL);
 	Assert(WorkerTasksSharedState->taskHashTrancheId != 0);
 
 	if (prev_shmem_startup_hook != NULL)

src/backend/distributed/worker/task_tracker_protocol.c

@@ -189,7 +189,7 @@ task_tracker_cleanup_job(PG_FUNCTION_ARGS)
 	 */
 	LWLockAcquire(&WorkerTasksSharedState->taskHashLock, LW_EXCLUSIVE);
 
-	hash_seq_init(&status, WorkerTasksSharedState->taskHash);
+	hash_seq_init(&status, TaskTrackerTaskHash);
 
 	currentTask = (WorkerTask *) hash_seq_search(&status);
 	while (currentTask != NULL)
@@ -415,8 +415,7 @@ CleanupTask(WorkerTask *workerTask)
 	}
 
 	/* remove the task from the shared hash */
-	taskRemoved = hash_search(WorkerTasksSharedState->taskHash, hashKey, HASH_REMOVE,
-							  NULL);
+	taskRemoved = hash_search(TaskTrackerTaskHash, hashKey, HASH_REMOVE, NULL);
 	if (taskRemoved == NULL)
 	{
 		ereport(FATAL, (errmsg("worker task hash corrupted")));

src/include/distributed/task_tracker.h

@@ -101,9 +101,6 @@ typedef struct WorkerTask
  */
 typedef struct WorkerTasksSharedStateData
 {
-	/* Hash table shared by the task tracker and task tracker protocol functions */
-	HTAB *taskHash;
-
 	/* Lock protecting workerNodesHash */
 	int taskHashTrancheId;
 #if (PG_VERSION_NUM >= 100000)
@@ -123,6 +120,7 @@ extern int MaxTaskStringSize;
 
 /* State shared by the task tracker and task tracker protocol functions */
 extern WorkerTasksSharedStateData *WorkerTasksSharedState;
+extern HTAB *TaskTrackerTaskHash;
 
 /* Entry point */
 extern void TaskTrackerMain(Datum main_arg);