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From "Jark Wu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-5047) Add sliding group-windows for batch tables
Date Thu, 10 Nov 2016 11:54:58 GMT

    [ https://issues.apache.org/jira/browse/FLINK-5047?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15653869#comment-15653869

Jark Wu commented on FLINK-5047:

Hi [~fhueske] Agree. I think the first approach can be easily supported after FLINK-4692 resolved.

Regarding to 
it a) is based on the implementation that supports non-combinable aggregates (which is required
in any case) 

If I understand correctly, the third approach doesn't support non-combinable aggregates  such
as median, right ?  It's only an optimization for pre-aggregation which is better than approach-2
, right?  

> Add sliding group-windows for batch tables
> ------------------------------------------
>                 Key: FLINK-5047
>                 URL: https://issues.apache.org/jira/browse/FLINK-5047
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Table API & SQL
>            Reporter: Jark Wu
> Add Slide group-windows for batch tables as described in [FLIP-11|https://cwiki.apache.org/confluence/display/FLINK/FLIP-11%3A+Table+API+Stream+Aggregations].
> There are two ways to implement sliding windows for batch:
> 1. replicate the output in order to assign keys for overlapping windows. This is probably
the more straight-forward implementation and supports any aggregation function but blows up
the data volume.
> 2. if the aggregation functions are combinable / pre-aggregatable, we can also find the
largest tumbling window size from which the sliding windows can be assembled. This is basically
the technique used to express sliding windows with plain SQL (GROUP BY + OVER clauses). For
a sliding window Slide(10 minutes, 2 minutes) this would mean to first compute aggregates
of non-overlapping (tumbling) 2 minute windows and assembling consecutively 5 of these into
a sliding window (could be done in a MapPartition with sorted input). The implementation could
be done as an optimizer rule to split the sliding aggregate into a tumbling aggregate and
a SQL WINDOW operator. Maybe it makes sense to implement the WINDOW clause first and reuse
this for sliding windows.
> 3. There is also a third, hybrid solution: Doing the pre-aggregation on the largest non-overlapping
windows (as in 2) and replicating these results and processing those as in the 1) approach.
The benefits of this is that it a) is based on the implementation that supports non-combinable
aggregates (which is required in any case) and b) that it does not require the implementation
of the SQL WINDOW operator. Internally, this can be implemented again as an optimizer rule
that translates the SlidingWindow into a pre-aggregating TublingWindow and a final SlidingWindow
(with replication).
> see FLINK-4692 for more discussion

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