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Date: Tue, 22 Sep 2015 00:40:04 +0000 (UTC)
From: "ASF GitHub Bot (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (ACCUMULO-2232) Combiners can cause deleted data
 to come back
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    [ https://issues.apache.org/jira/browse/ACCUMULO-2232?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14901683#comment-14901683 ] 

ASF GitHub Bot commented on ACCUMULO-2232:
------------------------------------------

GitHub user keith-turner opened a pull request:

    https://github.com/apache/accumulo/pull/47

    ACCUMULO-2232 Added options to Combiner for handling deletes

    
You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/keith-turner/accumulo ACCUMULO-2232

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/accumulo/pull/47.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #47
    
----
commit 0ca928603078ed1698186515325b20eb98b4515a
Author: Keith Turner <kturner@apache.org>
Date:   2015-09-21T19:23:18Z

    ACCUMULO-2232 Added options to Combiner for handling deletes

----


> Combiners can cause deleted data to come back
> ---------------------------------------------
>
>                 Key: ACCUMULO-2232
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-2232
>             Project: Accumulo
>          Issue Type: Bug
>          Components: client, tserver
>            Reporter: John Vines
>
> The case-
> 3 files with-
> * 1 with a key, k, with timestamp 0, value 3
> * 1 with a delete of k with timestamp 1
> * 1 with k with timestamp 2, value 2
> The column of k has a summing combiner set on it. The issue here is that depending on how the major compactions play out, differing values with result. If all 3 files compact, the correct value of 2 will result. However, if 1 & 3 compact first, they will aggregate to 5. And then the delete will fall after the combined value, resulting in the result 5 to persist.
> First and foremost, this should be documented. I think to remedy this, combiners should only be used on full MajC, not not full ones. This may necessitate a special flag or a new combiner that implemented the proper semantics.


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