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https://issues.apache.org/jira/browse/HIVE-16886?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16143221#comment-16143221
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Na Li commented on HIVE-16886:
------------------------------
We did testing and it shows when executing SQL command in transactions
concurrently, the result is determined by the order of SQL execution order (if
SQL1 is executed before SQL2 and both set value of the same column in the same
row and same table, the result is the same as the value set by SQL2, i.e., the
last executed wins). The result is NOT determined by the transaction commit
order.
When Sentry gets notifications and apply them, it should apply them in the same
order as hive applies those changes. Otherwise, sentry may end up getting
different path state from what hive has. It is undesirable.
In order to achieve consistent synchronization, could hive make sure that the
event ID order is the same as the path sql execution order? One way to achieve
this is to keep the notification log in the same transaction of the path sql
statement, and the order in the transaction is to persist notification log
after the path SQL statement
{
Execute path SQL statements,
Persist notification log
}
> 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
> Assignee: anishek
> Attachments: datastore-identity-holes.diff, HIVE-16886.1.patch,
> HIVE-16886.2.patch
>
>
> 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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