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https://issues.apache.org/jira/browse/SOLR-8241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15558485#comment-15558485
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Shawn Heisey commented on SOLR-8241:
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Taking a look at this today.
Would you be able to build some tests? I can copy the existing LFUCache tests
and modify them until they pass, but it would be better for somebody who knows
how the cache is *supposed* to work to engineer those tests so they check for
what *should* happen. Best possible result would be that my assumptions for
LFUCache will hold without changes, but that is probably not likely.
New cache warming loses old frequency information, as I already mentioned
earlier. I suspect that even without this being preserved, we're likely to see
a generally higher hitrate than LRU. I would like to preserve this information
if possible, but I don't view it as a blocker.
> Evaluate W-TinyLfu cache
> ------------------------
>
> Key: SOLR-8241
> URL: https://issues.apache.org/jira/browse/SOLR-8241
> Project: Solr
> Issue Type: Wish
> Components: search
> Reporter: Ben Manes
> Priority: Minor
> Attachments: SOLR-8241.patch
>
>
> 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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