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From "sunjincheng (JIRA)" <j...@apache.org>
Subject [jira] [Created] (FLINK-7465) Add build-in BloomFilterCount on TableAPI&SQL
Date Thu, 17 Aug 2017 07:54:00 GMT
sunjincheng created FLINK-7465:
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             Summary: Add build-in BloomFilterCount on TableAPI&SQL
                 Key: FLINK-7465
                 URL: https://issues.apache.org/jira/browse/FLINK-7465
             Project: Flink
          Issue Type: Sub-task
          Components: Table API & SQL
            Reporter: sunjincheng
            Assignee: sunjincheng


In this JIRA. use BloomFilter to implement counting functions.
BloomFilter Algorithm description:
An empty Bloom filter is a bit array of m bits, all set to 0. There must also be k different
hash functions defined, each of which maps or hashes some set element to one of the m array
positions, generating a uniform random distribution. Typically, k is a constant, much smaller
than m, which is proportional to the number of elements to be added; the precise choice of
k and the constant of proportionality of m are determined by the intended false positive rate
of the filter.

To add an element, feed it to each of the k hash functions to get k array positions. Set the
bits at all these positions to 1.

To query for an element (test whether it is in the set), feed it to each of the k hash functions
to get k array positions. If any of the bits at these positions is 0, the element is definitely
not in the set – if it were, then all the bits would have been set to 1 when it was inserted.
If all are 1, then either the element is in the set, or the bits have by chance been set to
1 during the insertion of other elements, resulting in a false positive.

An example of a Bloom filter, representing the set {x, y, z}. The colored arrows show the
positions in the bit array that each set element is mapped to. The element w is not in the
set {x, y, z}, because it hashes to one bit-array position containing 0. For this figure,
m = 18 and k = 3. The sketch as follows:
!https://en.wikipedia.org/wiki/Bloom_filter#/media/File:Bloom_filter.svg!



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