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From Sergio Peña (JIRA) <j...@apache.org>
Subject [jira] [Created] (HIVE-16164) Provide mechanism for passing HMS notification ID between transactional and non-transactional listeners.
Date Fri, 10 Mar 2017 00:17:37 GMT
Sergio Peña created HIVE-16164:
----------------------------------

             Summary: Provide mechanism for passing HMS notification ID between transactional
and non-transactional listeners.
                 Key: HIVE-16164
                 URL: https://issues.apache.org/jira/browse/HIVE-16164
             Project: Hive
          Issue Type: Improvement
          Components: Metastore
            Reporter: Sergio Peña
            Assignee: Sergio Peña


The HMS DB notification listener currently stores an event ID on the HMS backend DB so that
external applications (such as backup apps) can request incremental notifications based on
the last event ID requested.

The HMS DB notification and backup applications are asynchronous. However, there are sometimes
that applications may be required to be in sync with the latest HMS event in order to process
an action. These applications will provide a listener implementation that is called by the
HMS after an HMS transaction happened.

The problem is that the listener running after the transaction (or during the non-transactional
context) may need the DB event ID in order to sync all events happened previous to that event
ID, but this ID is never passed to the non-transactional listeners.

We can pass this event information through the EnvironmentContext found on each ListenerEvent
implementations (such as CreateTableEvent), and send the EnvironmentContext to the non-transactional
listeners to get the event ID.

The DbNotificactionListener already knows the event ID after calling the ObjectStore.addNotificationEvent().
We just need to set this event ID to the EnvironmentContext from each of the event notifications
and make sure that this EnvironmentContext is sent to the non-transactional listeners.

Here's the code example when creating a table on {{create_table_core}}:

{noformat}
 ms.createTable(tbl);

  if (transactionalListeners.size() > 0) {
    CreateTableEvent createTableEvent = new CreateTableEvent(tbl, true, this);
    createTableEvent.setEnvironmentContext(envContext);
    for (MetaStoreEventListener transactionalListener : transactionalListeners) {
      transactionalListener.onCreateTable(createTableEvent);         // <- Here the notification
ID is generated
    }
  }

  success = ms.commitTransaction();
} finally {
  if (!success) {
    ms.rollbackTransaction();
    if (madeDir) {
      wh.deleteDir(tblPath, true);
    }
  }
  for (MetaStoreEventListener listener : listeners) {
    CreateTableEvent createTableEvent =
        new CreateTableEvent(tbl, success, this);
    createTableEvent.setEnvironmentContext(envContext);
    listener.onCreateTable(createTableEvent);                        // <- Here we would
like to consume notification ID
  }
{noformat}

We could use a specific key name that will be used on the EnvironmentContext, such as DB_NOTIFICATION_EVENT_ID.



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