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sunjincheng commented on FLINK7465:

I close this issue because I notices that current implementation is high demanding for CPU,
And we can do the same thing using distinct count.
> Add buildin BloomFilterCount on TableAPI&SQL
> 
>
> Key: FLINK7465
> URL: https://issues.apache.org/jira/browse/FLINK7465
> Project: Flink
> Issue Type: Subtask
> 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 bitarray position containing 0. For this figure,
m = 18 and k = 3. The sketch as follows:
> !bloomfilter.png!
> Reference:
> 1. https://en.wikipedia.org/wiki/Bloom_filter
> 2. https://github.com/apache/hive/blob/master/storageapi/src/java/org/apache/hive/common/util/BloomFilter.java
> Hi [~fhueske] [~twalthr] I appreciated if you can give me some advice. :)

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