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https://issues.apache.org/jira/browse/SOLR-14904?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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David Smiley reassigned SOLR-14904:
-----------------------------------

    Assignee: David Smiley

> Don't use documentCache for large result sets
> ---------------------------------------------
>
>                 Key: SOLR-14904
>                 URL: https://issues.apache.org/jira/browse/SOLR-14904
>             Project: Solr
>          Issue Type: Improvement
>      Security Level: Public(Default Security Level. Issues are Public) 
>            Reporter: David Smiley
>            Assignee: David Smiley
>            Priority: Major
>
> Some users ask Solr to return many documents (high rows param), even though 
> this is an anti-pattern.  Sometimes there is some sense to it, and even Solr 
> itself will do it in some cases like "bin/solr export" and perhaps some 
> streaming-expressions cases.  If there is a documentCache, these queries have 
> a tendency to completely thrash it -- dump it and fill it with poor cache 
> candidates.  I've even seen the cache's existence for such queries become a 
> bottleneck of the query -- granted for the now old LRUCache and in a 
> particularly high abuse-case.
> I propose that if the number of documents to be returned is above some 
> fraction of the documentCache's size limit, then don't use the documentCache 
> at all.  Maybe half size is sufficient?  Or quarter-size?  Maybe at least 
> queryWindowSize big (thus at least 20 typically)?  I see in solrconfig a 
> queryResultMaxDocsCached option used for the queryResultCache but it could be 
> made to apply to populating the documentCache as well.  Code default is 
> infinite but the default and most configs set to 200.



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