[jira] [Commented] (KYLIN-2221) rethink on KYLIN-1684

["hongbin ma (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KYLIN-2221?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15685767#comment-15685767 ] 

hongbin ma commented on KYLIN-2221:
-----------------------------------

In KYLIN-1684 we changed query behavior on empty segments, to cater for some rare scenarios described in KYLIN-1684. The reason why I call it "rare scenario" is because it only happens when you shutdown your hadoop history server, which looks to me very unreasonable.

Later we found the change was too costly to maintain, because we never know what exceptions will meet when querying an empty segment. 

TO save the troubles we'll go back before KYLIN-1684,  if a segment's input number is 0, we SUGGEST to skip querying the segment at all.  Plus, we'll leave a toggle called "kylin.query.skip-empty-segments". Users who share the same situation like the report of KYLIN-1864 can disable the toggle to enforce query for the look-like-empty-but-not-empty segment anyway. However, this is not suggested because when you later query on a "really empty" segment, you may encounter unexpected exceptions.



> rethink on KYLIN-1684
> ---------------------
>
>                 Key: KYLIN-2221
>                 URL: https://issues.apache.org/jira/browse/KYLIN-2221
>             Project: Kylin
>          Issue Type: Improvement
>            Reporter: hongbin ma
>            Assignee: hongbin ma
>




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