Sergio Peña created HIVE-16886: ---------------------------------- Summary: HMS log notifications may have duplicated event IDs if multiple HMS are running concurrently Key: HIVE-16886 URL: https://issues.apache.org/jira/browse/HIVE-16886 Project: Hive Issue Type: Bug Components: Hive, Metastore Reporter: Sergio Peña
When running multiple Hive Metastore servers and DB notifications are enabled, I could see that notifications can be persisted with a duplicated event ID. This does not happen when running multiple threads in a single HMS node due to the locking acquired on the DbNotificationsLog class, but multiple HMS could cause conflicts. The issue is in the ObjectStore#addNotificationEvent() method. The event ID fetched from the datastore is used for the new notification, incremented in the server itself, then persisted or updated back to the datastore. If 2 servers read the same ID, then these 2 servers write a new notification with the same ID. The event ID is not unique nor a primary key. Here's a test case using the TestObjectStore class that confirms this issue: {noformat} @Test public void testConcurrentAddNotifications() throws ExecutionException, InterruptedException { final int NUM_THREADS = 2; CountDownLatch countIn = new CountDownLatch(NUM_THREADS); CountDownLatch countOut = new CountDownLatch(1); HiveConf conf = new HiveConf(); conf.setVar(HiveConf.ConfVars.METASTORE_EXPRESSION_PROXY_CLASS, MockPartitionExpressionProxy.class.getName()); ExecutorService executorService = Executors.newFixedThreadPool(NUM_THREADS); FutureTask<Void> tasks[] = new FutureTask[NUM_THREADS]; for (int i=0; i<NUM_THREADS; i++) { final int n = i; tasks[i] = new FutureTask<Void>(new Callable<Void>() { @Override public Void call() throws Exception { ObjectStore store = new ObjectStore(); store.setConf(conf); NotificationEvent dbEvent = new NotificationEvent(0, 0, EventMessage.EventType.CREATE_DATABASE.toString(), "CREATE DATABASE DB" + n); System.out.println("ADDING NOTIFICATION"); countIn.countDown(); countOut.await(); store.addNotificationEvent(dbEvent); System.out.println("FINISH NOTIFICATION"); return null; } }); executorService.execute(tasks[i]); } countIn.await(); countOut.countDown(); for (int i = 0; i < NUM_THREADS; ++i) { tasks[i].get(); } NotificationEventResponse eventResponse = objectStore.getNextNotification(new NotificationEventRequest()); Assert.assertEquals(2, eventResponse.getEventsSize()); Assert.assertEquals(1, eventResponse.getEvents().get(0).getEventId()); // This fails because the next notification has an event ID = 1 Assert.assertEquals(2, eventResponse.getEvents().get(1).getEventId()); } {noformat} The last assertion fails expecting an event ID 1 instead of 2. -- This message was sent by Atlassian JIRA (v6.4.14#64029)