c33b8dcbf6
Add the implementation for ApproximateCountDistinct to SparkSql. We use the HyperLogLog algorithm implemented in stream-lib, and do the count in two phases: 1) counting the number of distinct elements in each partitions, and 2) merge the HyperLogLog results from different partitions. A simple serializer and test cases are added as well. Author: larvaboy <larvaboy@gmail.com> Closes #737 from larvaboy/master and squashes the following commits: bd8ef3f [larvaboy] Add support of user-provided standard deviation to ApproxCountDistinct. 9ba8360 [larvaboy] Fix alignment and null handling issues. 95b4067 [larvaboy] Add a test case for count distinct and approximate count distinct. f57917d [larvaboy] Add the parser for the approximate count. a2d5d10 [larvaboy] Add ApproximateCountDistinct aggregates and functions. 7ad273a [larvaboy] Add SparkSql serializer for HyperLogLog. 1d9aacf [larvaboy] Fix a minor typo in the toString method of the Count case class. 653542b [larvaboy] Fix a couple of minor typos. |
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