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Date: Wed, 26 Nov 2014 01:12:13 +0000 (UTC)
From: "Vijay (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
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Subject: [jira] [Commented] (CASSANDRA-7438) Serializing Row cache
 alternative (Fully off heap)
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    [ https://issues.apache.org/jira/browse/CASSANDRA-7438?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14225532#comment-14225532 ] 

Vijay commented on CASSANDRA-7438:
----------------------------------

{quote}
so each segment would be a 4-byte lock
{quote}
Are you talking about setting Just setting 1 for lock and 0 for unlock?
Hmmm, alright thats doable... i am guessing you have already seen how ReentrantLock implements locking.

{quote}
The check on line 38 races with the assignment on line 39.
{quote}
I thought we discussed this already... Yeah that was suppose to take care by this comment "Next commit will have conditions instead (similar to C implementation).", have not committed it yet :)

> 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
>
>
> 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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