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  1. Accumulo
  2. ACCUMULO-2232

Combiners can cause deleted data to come back

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    Details

    • Type: Bug
    • Status: Resolved
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 1.6.5, 1.7.1, 1.8.0
    • Component/s: client, tserver
    • Labels:
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      Description

      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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              • Assignee:
                kturner Keith Turner
                Reporter:
                vines John Vines
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