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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-11452) Cache implementation using LIRS eviction for in-process page cache
Date Tue, 12 Apr 2016 21:44:26 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-11452?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15238051#comment-15238051
] 

Benedict commented on CASSANDRA-11452:
--------------------------------------

bq.  retain hash collisions

For this to be a problem it would have to be a collision on all hashes/buckets, which is probabilistically
unlikely - with a large enough cache and uniform hashes we can even calculate an expected
incidence.  Given the LRU arena will evict it in a predictable time we can also calculate
the fixed overhead for such mispredictions; it is unlikely to be very large (but would be
interesting - perhaps something the paper could have covered in its analysis of the overhead
per item).

Bear in mind also that - as opposed to LIRS which is an _eviction_ strategy - LFU only prevents
promotion to the LRU; the eviction strategy is still LRU, so it will not keep collisions,
only fail to filter them before they hit the (main) cache.


> Cache implementation using LIRS eviction for in-process page cache
> ------------------------------------------------------------------
>
>                 Key: CASSANDRA-11452
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11452
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Local Write-Read Paths
>            Reporter: Branimir Lambov
>            Assignee: Branimir Lambov
>
> Following up from CASSANDRA-5863, to make best use of caching and to avoid having to
explicitly marking compaction accesses as non-cacheable, we need a cache implementation that
uses an eviction algorithm that can better handle non-recurring accesses.



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