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Date: Tue, 22 Sep 2015 04:36:05 +0000 (UTC)
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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=14901918#comment-14901918 ] 

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

Github user joshelser commented on a diff in the pull request:

    https://github.com/apache/accumulo/pull/47#discussion_r40052512
  
    --- Diff: core/src/main/java/org/apache/accumulo/core/iterators/Combiner.java ---
    @@ -240,15 +299,18 @@ public void init(SortedKeyValueIterator<Key,Value> source, Map<String,String> op
         newInstance.setSource(getSource().deepCopy(env));
         newInstance.combiners = combiners;
         newInstance.combineAllColumns = combineAllColumns;
    +    newInstance.isPartialCompaction = isPartialCompaction;
    +    newInstance.deleteHandlingAction = deleteHandlingAction;
         return newInstance;
       }
     
       @Override
       public IteratorOptions describeOptions() {
         IteratorOptions io = new IteratorOptions("comb", "Combiners apply reduce functions to multiple versions of values with otherwise equal keys", null, null);
    -    io.addNamedOption(ALL_OPTION, "set to true to apply Combiner to every column, otherwise leave blank. if true, " + COLUMNS_OPTION
    -        + " option will be ignored.");
    +    io.addNamedOption(ALL_OPTION,
    --- End diff --
    
    Nit: unrelated formatting.


> 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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