[jira] [Commented] (FLINK-1297) Add support for tracking statistics of intermediate results

["Andreas Kunft (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-1297?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14231722#comment-14231722 ] 

Andreas Kunft commented on FLINK-1297:
--------------------------------------

I would suggest to have a look at the HyperLogLog algorithm for the cardinality estimation.
It seems to offer a good tradeoff between accuracy and size.

> Add support for tracking statistics of intermediate results
> -----------------------------------------------------------
>
>                 Key: FLINK-1297
>                 URL: https://issues.apache.org/jira/browse/FLINK-1297
>             Project: Flink
>          Issue Type: Improvement
>          Components: Distributed Runtime
>            Reporter: Alexander Alexandrov
>            Assignee: Alexander Alexandrov
>             Fix For: 0.8-incubating
>
>   Original Estimate: 1,008h
>  Remaining Estimate: 1,008h
>
> One of the major problems related to the optimizer at the moment is the lack of proper statistics.
> With the introduction of staged execution, it is possible to instrument the runtime code with a statistics facility that collects the required information for optimizing the next execution stage.
> I would therefore like to contribute code that can be used to gather basic statistics for the (intermediate) result of dataflows (e.g. min, max, count, count distinct) and make them available to the job manager.
> Before I start, I would like to hear some feedback form the other users.
> In particular, to handle skew (e.g. on grouping) it might be good to have some sort of detailed sketch about the key distribution of an intermediate result. I am not sure whether a simple histogram is the most effective way to go. Maybe somebody would propose another lightweight sketch that provides better accuracy.



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