[jira] [Commented] (CASSANDRA-5939) Cache Providers calculate very different row sizes

["Vijay (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-5939?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13753061#comment-13753061 ] 

Vijay commented on CASSANDRA-5939:
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Chris, Not sure if i understand the question/issue right... 

If the question is whats the difference between SC and CLHM in terms of memory overhead?

CLHM Entry's (Key and Value) weight is calculated, where as SC we only weigh the values (which is off-heap) and we don't weigh the size of the keys in the heap (since it is kind of hybrid foot print's).
CLHM has java's Object overhead (look https://issues.apache.org/jira/browse/CASSANDRA-4860?focusedCommentId=13632991&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13632991), SC we Encode the bytes hence it will be considerably low overhead of value's in memory. Your milage also may vary depending on the size of the columns.
                
> Cache Providers calculate very different row sizes
> --------------------------------------------------
>
>                 Key: CASSANDRA-5939
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5939
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>         Environment: 1.2.8
>            Reporter: Chris Burroughs
>            Assignee: Vijay
>
> Took the same production node and bounced it 4 times comparing version and cache provider.  ConcurrentLinkedHashCacheProvider and SerializingCacheProvider produce very different results resulting in an order of magnitude difference in rows cached.  In all cases the row cache size was 2048 MB.  Hit rate is provided for color, but entries & size are the important part.
> 1.2.8 ConcurrentLinkedHashCacheProvider:
>  * entries: 23,217
>  * hit rate: 43%
>  * size: 2,147,398,344
> 1.2.8 about 20 minutes of SerializingCacheProvider:
>  * entries: 221,709
>  * hit rate: 68%
>  * size: 18,417254
> 1.2.5 ConcurrentLinkedHashCacheProvider:
>  * entries: 25,967
>  * hit rate: ~ 50%
>  * size:  2,147,421,704
> 1.2.5 about 20 minutes of SerializingCacheProvider:
>  * entries: 228,457
>  * hit rate: ~ 70%
>  * size: 19,070,315
> A related(?) problem is that the ConcurrentLinkedHashCacheProvider sizes seem to be highly variable.  Digging up the values for 5 different nodes in the cluster using ConcurrentLinkedHashCacheProvider shows a wide variance in number of entries:
>  * 12k
>  * 444k
>  * 10k
>  * 25k
>  * 25k

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