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https://issues.apache.org/jira/browse/SOLR-8241?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15137111#comment-15137111
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Shawn Heisey commented on SOLR-8241:
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If this proves to be advantageous, it would be my recommendation to replace
LFUCache, not add an entirely new implementation. I would also suggest that we
build something into the tests that will help us evaluate the performance of
the various cache implementations, to determine if a later step should be to
change the example configs to use LFUCache. In general, I believe LFU to be a
more viable eviction method for Solr than LRU, inherently more capable of
reaching a higher hit ratio, but we need an efficient implementation.
It looks like this is a master-only patch. I can see some code that looks like
it's for Java 8 only, both before and after the patch. I do not understand
this part of the patch, because I do not have any idea how to use the new
capabilities in Java 8, or what those new capabilities actually do:
{code}
- RemovalListener<BlockCacheKey,BlockCacheLocation> listener =
- notification -> releaseLocation(notification.getValue());
+ RemovalListener<BlockCacheKey,BlockCacheLocation> listener =
+ (key, value, cause) -> releaseLocation(value);
{code}
The code that is patched above does not exist in branch_5x. It's not a problem
to have a master-only patch, just something notable.
As for the actual implementation: That is going to take me longer to digest.
My free time is in short supply.
> 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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