[jira] [Created] (HIVE-16886) HMS log notifications may have duplicated event IDs if multiple HMS are running concurrently

["Sergio Peña (JIRA)" <ji...@apache.org>]

Sergio Peña created HIVE-16886:
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             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. 



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