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From "Ben Manes (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-11452) Cache implementation using LIRS eviction for in-process page cache
Date Fri, 15 Apr 2016 07:50:25 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-11452?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15242600#comment-15242600
] 

Ben Manes commented on CASSANDRA-11452:
---------------------------------------

I chatted with Roy about this problem and he's going to ponder it as well.

I thought about this and toyed with the code a little. 
- You're right that my hash detection is very weak and poor enough probably not bother.
- I do wish Java would add {{longHashCode}} to Object, finally. Its a good improvement for
other platforms.
- Your random walk requires that the attacker can exploit the full walking distance (last
16) potential victims. The stepwise walk means it could exploit fewer (e.g. 8) to have an
effect, but have to restart when the cache jitters out. If quantified it might prove the attack
impractical.
- Moving the victim to the MRU position after an admission is rejected works at a small cost
to the hit rate. This could be reduced by adding a smaller segment (e.g. bottom N items) so
that we don't degrade the recency effects.
- A sampled bloom filter of past rejections to bypass if TinyLFU present would probably work
well. I think it could also be used to adapt the window size or improve the hit rate by reducing
mispredictions. That would require a lot more work to evaluate, so impractical for the immediate
term.

My plan is to iterate on your random walk. I still think that the victim chosen should be
by the random walk and I haven't grokked your reason not to. I'm tired so maybe it will be
seem obvious later. The long week of production issues is making me feel pretty slow on this
one...

> 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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