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From "Keith Turner (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-2232) Combiners can cause deleted data to come back
Date Fri, 02 Oct 2015 17:12:27 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-2232?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14941419#comment-14941419
] 

Keith Turner commented on ACCUMULO-2232:
----------------------------------------

[~ctubbsii] thanks for updating it.   I am thinking this ticket can be closed, ACCUMULO-4011
outlines further follow on work.  If there is any other follow on work, then should probably
open specific tickets.

> 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
>            Assignee: Keith Turner
>             Fix For: 1.6.5, 1.7.1, 1.8.0
>
>          Time Spent: 20m
>  Remaining Estimate: 0h
>
> 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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