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https://issues.apache.org/jira/browse/HIVE-16886?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16105271#comment-16105271
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Sergio Peña commented on HIVE-16886:
------------------------------------
[~anishek] [~thejas] While running some tests with duplicated events IDs in HMS
HA mode, I see that the NL_ID is never duplicated and is always consecutive and
in order. Do you know why we're not using this ID instead? Seems more
consistent and better to use.
[~akolb] FYI
{noformat}
[hive1]> select NL_ID, EVENT_ID, EVENT_TIME, EVENT_TYPE, DB_NAME from
NOTIFICATION_LOG where NL_ID >= 5431 and NL_ID <= 5440;
+-------+----------+------------+-----------------+----------------------------------------+
| NL_ID | EVENT_ID | EVENT_TIME | EVENT_TYPE | DB_NAME
|
+-------+----------+------------+-----------------+----------------------------------------+
| 5431 | 5094 | 1501109698 | CREATE_DATABASE |
metastore_test_db_HIVE_HIVEMETASTORE_2 |
| 5432 | 5097 | 1501109698 | CREATE_TABLE |
metastore_test_db_HIVE_HIVEMETASTORE_2 |
| 5433 | 5098 | 1501109699 | ADD_PARTITION |
metastore_test_db_HIVE_HIVEMETASTORE_2 |
| 5434 | 5101 | 1501109791 | DROP_TABLE |
metastore_test_db_HIVE_HIVEMETASTORE_2 |
| 5435 | 5104 | 1501109792 | DROP_DATABASE |
metastore_test_db_HIVE_HIVEMETASTORE_2 |
| 5436 | 5096 | 1501109698 | CREATE_DATABASE |
metastore_test_db_HIVE_HIVEMETASTORE_1 |
| 5437 | 5097 | 1501109698 | CREATE_TABLE |
metastore_test_db_HIVE_HIVEMETASTORE_1 |
| 5438 | 5100 | 1501109699 | ADD_PARTITION |
metastore_test_db_HIVE_HIVEMETASTORE_1 |
| 5439 | 5102 | 1501109791 | DROP_TABLE |
metastore_test_db_HIVE_HIVEMETASTORE_1 |
| 5440 | 5105 | 1501109792 | DROP_DATABASE |
metastore_test_db_HIVE_HIVEMETASTORE_1 |
+-------+----------+------------+-----------------+----------------------------------------+
{noformat}
> 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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