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https://issues.apache.org/jira/browse/CASSANDRA-7438?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14228397#comment-14228397
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Benedict commented on CASSANDRA-7438:
-------------------------------------
I suspect segmenting the table at a finer granularity, so that each segment is
maintained with mutual exclusivity, would achieve better percentiles in both
cases due to keeping the maximum resize cost down. We could settle for a
separate LRU-q per segment, even, to keep the complexity of this code down
significantly - it is unlikely having a global LRU-q is significantly more
accurate at predicting reuse than ~128 of them. It would also make it much
easier to improve the replacement strategy beyond LRU, which would likely yield
a bigger win for performance than any potential loss from reduced concurrency.
The critical section for reads could be kept sufficiently small that
competition would be very unlikely with the current state of C*, by performing
the deserialization outside of it. There's a good chance this would yield a net
positive performance impact, by reducing the cost per access without increasing
the cost due to contention measurably (because contention would be infrequent).
> Serializing Row cache alternative (Fully off heap)
> --------------------------------------------------
>
> Key: CASSANDRA-7438
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7438
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Environment: Linux
> Reporter: Vijay
> Assignee: Vijay
> Labels: performance
> Fix For: 3.0
>
> Attachments: 0001-CASSANDRA-7438.patch, tests.zip
>
>
> Currently SerializingCache is partially off heap, keys are still stored in
> JVM heap as BB,
> * There is a higher GC costs for a reasonably big cache.
> * Some users have used the row cache efficiently in production for better
> results, but this requires careful tunning.
> * Overhead in Memory for the cache entries are relatively high.
> So the proposal for this ticket is to move the LRU cache logic completely off
> heap and use JNI to interact with cache. We might want to ensure that the new
> implementation match the existing API's (ICache), and the implementation
> needs to have safe memory access, low overhead in memory and less memcpy's
> (As much as possible).
> We might also want to make this cache configurable.
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