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https://issues.apache.org/jira/browse/DRILL-229?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13778079#comment-13778079
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Jacques Nadeau commented on DRILL-229:
--------------------------------------

Nice! Looks right on the money.  
                
> Build a Merging Recevier
> ------------------------
>
>                 Key: DRILL-229
>                 URL: https://issues.apache.org/jira/browse/DRILL-229
>             Project: Apache Drill
>          Issue Type: New Feature
>            Reporter: Jacques Nadeau
>            Assignee: Ben Becker
>
> Build a merging receiver operator which combines a number of incoming buffers 
> into a single output stream by merging the streams based on equality of one 
> or more expressions.
> The following example illustrates a distributed count operation, where each 
> remote fragment counts a subset of the data and the root fragment produces a 
> sum of each count aggregate.
> h4. Data Flow
> {noformat}
> RecordReader
>   |
>   +-> Sort
>        |
>        +-> StreamingAggregate(COUNT)
>               |
>               +-> MergingPartitionExchange
>                      |
>                      +-> StreamingAggregate(SUM)
>                             |
>                             +-> UnionExchange
>                                    |
>                                    +-> Screen
> {noformat}
> h4. Control Flow
> {noformat}
> Root Fragment
> -------------
> Screen
>    |
>    +->UnionExchange
>          | | |
>          | | +->AggSum
>          | |      |
>          | |      +->MergingReceiver
>          | |
>          | +--->AggSum
>          |        |
>          |        +->MergingReceiver
>          |
>          +----->AggSum
>                   |
>                   +->MergingReceiver
>              ...
> Remote Fragment
> ---------------
> PartitionSender
>        |
>        +->AggCount
>              |
>              +->Sort
>                  |
>                  +->Reader
> {noformat}

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