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https://issues.apache.org/jira/browse/SOLR-8922?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15220342#comment-15220342
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Jeff Wartes commented on SOLR-8922:
-----------------------------------

Both of those appear to add capacity by declaring a new array and doing a 
System.arraycopy.
Wouldn't that just result in more space allocated and then thrown away?

> DocSetCollector can allocate massive garbage on large indexes
> -------------------------------------------------------------
>
>                 Key: SOLR-8922
>                 URL: https://issues.apache.org/jira/browse/SOLR-8922
>             Project: Solr
>          Issue Type: Improvement
>            Reporter: Jeff Wartes
>         Attachments: SOLR-8922.patch
>
>
> After reaching a point of diminishing returns tuning the GC collector, I 
> decided to take a look at where the garbage was coming from. To my surprise, 
> it turned out that for my index and query set, almost 60% of the garbage was 
> coming from this single line:
> https://github.com/apache/lucene-solr/blob/94c04237cce44cac1e40e1b8b6ee6a6addc001a5/solr/core/src/java/org/apache/solr/search/DocSetCollector.java#L49
> This is due to the simple fact that I have 86M documents in my shards. 
> Allocating a scratch array big enough to track a result set 1/64th of my 
> index (1.3M) is also almost certainly excessive, considering my 99.9th 
> percentile hit count is less than 56k.



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