Hadoop Common
  1. Hadoop Common
  2. HADOOP-3063

BloomMapFile - fail-fast version of MapFile for sparsely populated key space


    • Type: Improvement Improvement
    • Status: Closed
    • Priority: Major Major
    • Resolution: Fixed
    • Affects Version/s: 0.20.0
    • Fix Version/s: 0.20.0
    • Component/s: io
    • Labels:
    • Hadoop Flags:
    • Release Note:
      Introduced BloomMapFile subclass of MapFile that creates a Bloom filter from all keys.


      The need for this improvement arose when working with large ancillary MapFile-s (essentially used as external dictionaries). For each invokation of map() / reduce() it was necessary to perform several look-ups in these MapFile-s, and in case of sparsely populated key-space the cost of finding that a key is absent was too high.

      This patch implements a subclass of MapFile that creates a Bloom filter from all keys, so that accurate tests for absence of keys can be performed quickly and with 100% accuracy.

      Writer.append() operations update a DynamicBloomFilter, which is then serialized when the Writer is closed. This filter is loaded in memory when a Reader is created. Reader.get() operation first checks the filter for the key membership, and if the key is absent it immediately returns null without doing any further IO.

      1. bloommap.patch
        87 kB
        Andrzej Bialecki
      2. bloommap-v2.patch
        77 kB
        Andrzej Bialecki
      3. bloommap-v3.patch
        96 kB
        Andrzej Bialecki
      4. bloommap-v4.patch
        101 kB
        Andrzej Bialecki

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            • Assignee:
              Andrzej Bialecki
              Andrzej Bialecki
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