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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-5830) Resolve regressions to MapR DB from DRILL-5546
Date Wed, 04 Oct 2017 05:00:01 GMT

    [ https://issues.apache.org/jira/browse/DRILL-5830?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16190817#comment-16190817
] 

ASF GitHub Bot commented on DRILL-5830:
---------------------------------------

Github user paul-rogers commented on the issue:

    https://github.com/apache/drill/pull/968
  
    Thanks for the explanation! Bugs in the code are always a concern, but I personally prefer
to fix them rather than write more code that tries to work around potential, unknown bugs
in other code. (Working around known bugs is, of course, part of the game.)
    
    Sounds like we'll need to test the MapR-DB case for the conditions you identified; that
will tell is if the HBase solution (which seems to work now) can also be applied to MapR DB.


> Resolve regressions to MapR DB from DRILL-5546
> ----------------------------------------------
>
>                 Key: DRILL-5830
>                 URL: https://issues.apache.org/jira/browse/DRILL-5830
>             Project: Apache Drill
>          Issue Type: Bug
>    Affects Versions: 1.12.0
>            Reporter: Paul Rogers
>            Assignee: Paul Rogers
>             Fix For: 1.12.0
>
>
> DRILL-5546 added a number of fixes for empty batches. One part of the fix was for HBase.
Key changes:
> * Add code to expand wildcards in the planner. (i.e. SELECT *)
> * Remove support for wildcards in the HBase record reader.
> As noted in DRILL-5775, this change had the effect of breaking support for MapR-DB binary
(which is API compatible with HBase.) DRILL-5775 does this by expanding wildcards in the planner
for MapR DB as was done for HBase in DRILL-5546.
> Unfortunately, this change introduced other regressions into the code as described by
DRILL-5706.
> Investigation of those issues revealed that we should back out the original DRILL-5546
changes and go down a different route.
> As it turns out, HBase already had a project push-down rule that expanded wildcards.
However, that rule didn't work correctly some of the time. DRILL-5546 fixed that bug, ensuring
that wildcards are expanded (at least in the cases tested for this ticket.)
> The actual issue turned out to be a bug in the {{RecordBatchLoader}} class which did
not consider map contents when detecting schema change. As a result, results like (row_key,
cf\{}) were treated the same as (row_key, cf\{mycol}) and the actual data colums were discarded,
but randomly depending on batch arrival order.



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