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https://issues.apache.org/jira/browse/SOLR-3393?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13450611#comment-13450611
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Yonik Seeley commented on SOLR-3393:
------------------------------------

bq. ConcurrentLFUCache seems to provide no warranty that it will be able to 
evict entries as fast as they get inserted into the cache 

Correct, but the context in which this cache is used (things like filter 
caches, query caches, etc) ensure that this isn't really a problem in practice. 
 And since it's a cache, holding an extra entry briefly really doesn't have any 
negative effects.

I do think some sort of decay option is important, regardless of how it's 
implemented (and I never got a chance to look at the implementation here).

                
> Implement an optimized LFUCache
> -------------------------------
>
>                 Key: SOLR-3393
>                 URL: https://issues.apache.org/jira/browse/SOLR-3393
>             Project: Solr
>          Issue Type: Improvement
>          Components: search
>    Affects Versions: 3.6, 4.0-ALPHA
>            Reporter: Shawn Heisey
>            Priority: Minor
>             Fix For: 4.0
>
>         Attachments: SOLR-3393.patch, SOLR-3393.patch, SOLR-3393.patch, 
> SOLR-3393.patch, SOLR-3393.patch, SOLR-3393.patch, SOLR-3393.patch
>
>
> SOLR-2906 gave us an inefficient LFU cache modeled on 
> FastLRUCache/ConcurrentLRUCache.  It could use some serious improvement.  The 
> following project includes an Apache 2.0 licensed O(1) implementation.  The 
> second link is the paper (PDF warning) it was based on:
> https://github.com/chirino/hawtdb
> http://dhruvbird.com/lfu.pdf
> Using this project and paper, I will attempt to make a new O(1) cache called 
> FastLFUCache that is modeled on LRUCache.java.  This will (for now) leave the 
> existing LFUCache/ConcurrentLFUCache implementation in place.

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