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