Github user tammymendt commented on the pull request:
https://github.com/apache/flink/pull/605#issuecomment-127519735
Hey! So I've been using and testing this code throughout my master thesis.
Collecting count distinct makes jobs about 10% slower whereas collecting heavy
hitters can make a job be 20 to 50% slower (depending on the algorithm and the
distribution of the data). However this overhead is lower than that of using a
histogram accumulator (not to mention the histogram might not fit in memory). I
think it can be a nice addition to the code, specially since it does not affect
any core components.
The version that I pushed now uses a bunch of conditionals to check which
statistic is being collected. I know @fhueske did not really like this. I
implemented another version which avoids the conditionals by using a different
class for every type of statistic. I preferred to push this version though,
since it has been more thoroughly tested.
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