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From "sunjincheng (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (FLINK-7465) Add build-in BloomFilterCount on TableAPI&SQL
Date Thu, 17 Aug 2017 07:57:01 GMT

     [ https://issues.apache.org/jira/browse/FLINK-7465?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

sunjincheng updated FLINK-7465:
-------------------------------
    Attachment: bloomfilter.png

> 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
>         Attachments: bloomfilter.png
>
>
> 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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