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Date: Tue, 22 Sep 2015 04:39:04 +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=14901923#comment-14901923 ] 

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_r40052565
  
    --- Diff: core/src/test/java/org/apache/accumulo/core/iterators/user/CombinerTest.java ---
    @@ -786,4 +816,107 @@ public void testAdds() {
         assertEquals(LongCombiner.safeAdd(Long.MAX_VALUE - 5, 5), Long.MAX_VALUE);
       }
     
    +  private TreeMap<Key,Value> readAll(SortedKeyValueIterator<Key,Value> combiner) throws Exception {
    +    TreeMap<Key,Value> ret = new TreeMap<Key,Value>();
    +
    +    combiner.seek(new Range(), EMPTY_COL_FAMS, false);
    +
    +    while (combiner.hasTop()) {
    +      ret.put(new Key(combiner.getTopKey()), new Value(combiner.getTopValue()));
    +      combiner.next();
    +    }
    +
    +    return ret;
    +  }
    +
    +  private void runDeleteHandlingTest(TreeMap<Key,Value> input, TreeMap<Key,Value> expected, DeleteHandlingAction dha, IteratorEnvironment env)
    +      throws Exception {
    +    runDeleteHandlingTest(input, expected, dha, env, null);
    +  }
    +
    +  private void runDeleteHandlingTest(TreeMap<Key,Value> input, TreeMap<Key,Value> expected, DeleteHandlingAction dha, IteratorEnvironment env,
    +      String expectedLog) throws Exception {
    +    boolean deepCopy = expected == null;
    +
    +    StringWriter writer = new StringWriter();
    +    WriterAppender appender = new WriterAppender(new PatternLayout("%p, %m%n"), writer);
    +    Logger logger = Logger.getLogger(Combiner.class);
    +    boolean additivity = logger.getAdditivity();
    +    try {
    +      logger.addAppender(appender);
    +      logger.setAdditivity(false);
    +
    +      Combiner ai = new SummingCombiner();
    +
    +      IteratorSetting is = new IteratorSetting(1, SummingCombiner.class);
    +      SummingCombiner.setEncodingType(is, LongCombiner.StringEncoder.class);
    +      Combiner.setColumns(is, Collections.singletonList(new IteratorSetting.Column("cf001")));
    +      if (dha != null) {
    +        Combiner.setDeleteHandlingAction(is, dha);
    +      }
    +
    +      ai.init(new SortedMapIterator(input), is.getOptions(), env);
    +
    +      if (deepCopy)
    +        assertEquals(expected, readAll(ai.deepCopy(env)));
    +      assertEquals(expected, readAll(ai));
    +
    +    } finally {
    +      logger.removeAppender(appender);
    --- End diff --
    
    Glad to see the try/finally logger reset.


> 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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