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https://issues.apache.org/jira/browse/SOLR-7355?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14484300#comment-14484300
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Ben Manes commented on SOLR-7355:
---------------------------------
This ticket is not an attempt to advocate a competing project, but rather is a
notification that ConcurrentLinkedHashMap has reached its end-of-life and will
only receive maintenance updates. Similarly Guava's cache is in maintenance
mode, performance improvements are not accepted due to a lack of owner, and
Guava stay JDK6 due to Android. As the author or co-author of all three caching
libraries, this is the upgrade path that I recommend. Solr can instead choose
to stay as is or migrate to an alternative library.
Does Solr have performance tests? The before mentioned benchmarks show that
Caffeine has equivalent performance to CLHM v1.4.2. However, Solr uses the
older v1.2 dependency which typically performs reasonably well under
application load but much worse in a micro-benchmark. That's due to the
original focus on avoiding lock contention (Java 5 synchronizers were slow) and
later resolving GC pressure under synthetic stress tests. The evolutionary
improvements to Caffeine's algorithms mostly reduce memory usage and has only a
subtle impact on the performance profile.
Caffeine executes over 1.5 million unit tests and the changes pass Solr's test
suite. Any latent bugs will be addressed upon discovery.
> Java 8: ConcurrentLinkedHashMap -> Caffeine
> -------------------------------------------
>
> Key: SOLR-7355
> URL: https://issues.apache.org/jira/browse/SOLR-7355
> Project: Solr
> Issue Type: Task
> Reporter: Ben Manes
> Priority: Minor
> Attachments: SOLR-7355.patch
>
>
> When Solr transitions to requiring Java 8, please upgrade to Caffeine. The
> performance should be relatively the same. The per-instance memory usage
> should be smaller and Solr may decide to opt-in to use some of the additional
> features. The only drawback is that the jar size is larger due to code
> generation, though that may be trimmed over time and usually is not a concern
> for server-side applications.
> ConcurrentLinkedHashMap changes will continue to be minimal, even more so
> now, and driven by requests from Java 6 users unable to upgrade. Caffeine is
> ideally the upgrade path for Guava cache users too, which due to Android
> cannot be significantly modified.
> Caffeine: https://github.com/ben-manes/caffeine
> Benchmarks: https://github.com/ben-manes/caffeine/wiki/Benchmarks
> ConcurrentLinkedHashMap: https://code.google.com/p/concurrentlinkedhashmap
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