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

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

    [ https://issues.apache.org/jira/browse/IMPALA-8266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16781216#comment-16781216 ] 

Vihang Karajgaonkar commented on IMPALA-8266:
---------------------------------------------

Adding the review link

> 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
>            Priority: Major
>
> 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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