[jira] [Created] (IMPALA-8266) Event filtering logic may not filter all the events

["Vihang Karajgaonkar (JIRA)" <ji...@apache.org>]

Vihang Karajgaonkar created IMPALA-8266:
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             Summary: Event filtering logic may not filter all the events
                 Key: IMPALA-8266
                 URL: https://issues.apache.org/jira/browse/IMPALA-8266
             Project: IMPALA
          Issue Type: Sub-task
            Reporter: Vihang Karajgaonkar
            Assignee: Vihang Karajgaonkar


Here is a the logic to filter out create events from a given batch of events. 
{code}
Iterator<MetastoreEvent> it = metastoreEvents.iterator();
      // filter out the create events which has a corresponding drop event later
      int fromIndex = 0;
      int numFilteredEvents = 0;
      int inputSize = metastoreEvents.size();
      while (it.hasNext()) {
        MetastoreEvent current = it.next();
        if (fromIndex < metastoreEvents.size() && current.isRemovedAfter(
            metastoreEvents.subList(fromIndex + 1, metastoreEvents.size()))) {
          LOG.info(current.debugString("Filtering out this event since the object is "
              + "either removed or renamed later in the event stream"));
          it.remove();
          numFilteredEvents++;
        }
        fromIndex++;
      }
{code}

If the event list contains CREATE_DATABASE, CREATE_TABLE, DROP_TABLE, DROP_DATABASE events, it is possible that we only filter out CREATE_DATABASE event and not CREATE_TABLE event. This is because the {{fromIndex}} above gets incremented event iteration of the {{while}} loop and hence when it is evaluating if there is a inverse event later on in the stream, it starts to look from DROP_DATABASE event onwards.

The fix is simple, the fromIndex needs to be incremented only when the item from the list is not removed.



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