[jira] [Commented] (SOLR-14470) Add streaming expressions to /export handler

["David Smiley (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-14470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17111458#comment-17111458 ] 

David Smiley commented on SOLR-14470:
-------------------------------------

Sounds great but hopefully can be done in a layered way.  "/export" has a straight-forward purpose.  Adding aggregations _directly_ to it concerns me; it's then not some straight-forward component.

> Add streaming expressions to /export handler
> --------------------------------------------
>
>                 Key: SOLR-14470
>                 URL: https://issues.apache.org/jira/browse/SOLR-14470
>             Project: Solr
>          Issue Type: Improvement
>      Security Level: Public(Default Security Level. Issues are Public) 
>          Components: Export Writer, streaming expressions
>            Reporter: Andrzej Bialecki
>            Assignee: Andrzej Bialecki
>            Priority: Major
>
> Many streaming scenarios would greatly benefit from the ability to perform partial rollups (or other transformations) as early as possible, in order to minimize the amount of data that has to be sent from shards to the aggregating node.
> This can be implemented as a subset of streaming expressions that process the data directly inside each local {{ExportHandler}} and outputs only the records from the resulting stream. 
> Conceptually it would be similar to the way Hadoop {{Combiner}} works. As is the case with {{Combiner}}, because the input data is processed in batches there would be no guarantee that only 1 record per unique sort values would be emitted - in fact, in most cases multiple partial aggregations would be emitted. Still, in many scenarios this would allow reducing the amount of data to be sent by several orders of magnitude.



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