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https://issues.apache.org/jira/browse/SOLR-8241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16937851#comment-16937851
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Shawn Heisey commented on SOLR-8241:
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bq. Why does Solr have both limits enabled at once?
If I understand it all correctly, and it's always possible that I don't, I
think the idea is to allow a cache up to N entries, and if a smaller number of
entries consumes a specific byte size in heap requirements, to use the smaller
number instead.
I personally wouldn't have a problem with throwing an error if both limits are
specified, but that opinion might go against what others think.
> Evaluate W-TinyLfu cache
> ------------------------
>
> Key: SOLR-8241
> URL: https://issues.apache.org/jira/browse/SOLR-8241
> Project: Solr
> Issue Type: Improvement
> Components: search
> Reporter: Ben Manes
> Assignee: Andrzej Bialecki
> Priority: Major
> Fix For: master (9.0)
>
> Attachments: EvictionBenchmark.png, GetPutBenchmark.png,
> SOLR-8241.patch, SOLR-8241.patch, SOLR-8241.patch, SOLR-8241.patch,
> SOLR-8241.patch, caffeine-benchmark.txt, proposal.patch,
> solr_caffeine.patch.gz, solr_jmh_results.json
>
>
> SOLR-2906 introduced an LFU cache and in-progress SOLR-3393 makes it O(1).
> The discussions seem to indicate that the higher hit rate (vs LRU) is offset
> by the slower performance of the implementation. An original goal appeared to
> be to introduce ARC, a patented algorithm that uses ghost entries to retain
> history information.
> My analysis of Window TinyLfu indicates that it may be a better option. It
> uses a frequency sketch to compactly estimate an entry's popularity. It uses
> LRU to capture recency and operate in O(1) time. When using available
> academic traces the policy provides a near optimal hit rate regardless of the
> workload.
> I'm getting ready to release the policy in Caffeine, which Solr already has a
> dependency on. But, the code is fairly straightforward and a port into Solr's
> caches instead is a pragmatic alternative. More interesting is what the
> impact would be in Solr's workloads and feedback on the policy's design.
> https://github.com/ben-manes/caffeine/wiki/Efficiency
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