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https://issues.apache.org/jira/browse/SOLR-8281?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17200848#comment-17200848
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Gus Heck commented on SOLR-8281:
--------------------------------
This seems related to something I wanted to do for a client... I had reduce
with group() and I wanted to then feed the groups to an arbitrary streaming
expression for further processing, and have the result show up in the groups
(result would have been a matrix). Problem I stopped on was how to express the
stream to process the group without having a source (the source is the group).
> Add RollupMergeStream to Streaming API
> --------------------------------------
>
> Key: SOLR-8281
> URL: https://issues.apache.org/jira/browse/SOLR-8281
> Project: Solr
> Issue Type: Bug
> Reporter: Joel Bernstein
> Assignee: Joel Bernstein
> Priority: Major
>
> The RollupMergeStream merges the aggregate results emitted by the
> RollupStream on *worker* nodes.
> This is designed to be used in conjunction with the HashJoinStream to perform
> rollup Aggregations on the joined Tuples. The HashJoinStream will require the
> tuples to be partitioned on the Join keys. To avoid needing to repartition on
> the *group by* fields for the RollupStream, we can perform a merge of the
> rolled up Tuples coming from the workers.
> The construct would like this:
> {code}
> mergeRollup (...
> parallel (...
> rollup (...
> hashJoin (
> search(...),
> search(...),
> on="fieldA"
> )
> )
> )
> )
> {code}
> The pseudo code above would push the *hashJoin* and *rollup* to the *worker*
> nodes. The emitted rolled up tuples would be merged by the mergeRollup.
>
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