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https://issues.apache.org/jira/browse/SOLR-8220?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14977602#comment-14977602
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Yonik Seeley commented on SOLR-8220:
------------------------------------

bq. 3> shard2 returns its candidate top 10 to shard1. This return packet has 
the top 10 doc IDs and sort criteria.

We currently pull the sort criteria from the field comparators implementing the 
sort:
https://github.com/apache/lucene-solr/blob/trunk/solr/core/src/java/org/apache/solr/handler/component/QueryComponent.java#L638

> Read field from docValues for non stored fields
> -----------------------------------------------
>
>                 Key: SOLR-8220
>                 URL: https://issues.apache.org/jira/browse/SOLR-8220
>             Project: Solr
>          Issue Type: Improvement
>            Reporter: Keith Laban
>
> Many times a value will be both stored="true" and docValues="true" which 
> requires redundant data to be stored on disk. Since reading from docValues is 
> both efficient and a common practice (facets, analytics, streaming, etc), 
> reading values from docValues when a stored version of the field does not 
> exist would be a valuable disk usage optimization.
> The only caveat with this that I can see would be for multiValued fields as 
> they would always be returned sorted in the docValues approach. I believe 
> this is a fair compromise.
> I've done a rough implementation for this as a field transform, but I think 
> it should live closer to where stored fields are loaded in the 
> SolrIndexSearcher.
> Two open questions/observations:
> 1) There doesn't seem to be a standard way to read values for docValues, 
> facets, analytics, streaming, etc, all seem to be doing their own ways, 
> perhaps some of this logic should be centralized.
> 2) What will the API behavior be? (Below is my proposed implementation)
> Parameters for fl:
> - fl="docValueField"
>   -- return field from docValue if the field is not stored and in docValues, 
> if the field is stored return it from stored fields
> - fl="*"
>   -- return only stored fields
> - fl="+"
>    -- return stored fields and docValue fields
> 2a - would be easiest implementation and might be sufficient for a first 
> pass. 2b - is current behavior



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