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From "Pavel Yaskevich (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4937) CRAR improvements (object cache + CompressionMetadata chunk offset storage moved off-heap).
Date Sat, 10 Nov 2012 03:29:12 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4937?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13494545#comment-13494545
] 

Pavel Yaskevich commented on CASSANDRA-4937:
--------------------------------------------

bq. You are welcome to think how to do so without involving more then one file, I have exploited
lhf possibility 

That probably sounded confusing, I didn't mean to say that we are opening the same file multiple
times per one request, I was just trying to say that I wanted to keep caching changes as local
to CRAR as possible, without involving other "files" (or classes) in handling that cache,
which allowed to preserve open/close calls without involving anything specific to CRAR into
file handling.
                
> CRAR improvements (object cache + CompressionMetadata chunk offset storage moved off-heap).
> -------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-4937
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4937
>             Project: Cassandra
>          Issue Type: Improvement
>    Affects Versions: 1.1.6
>            Reporter: Pavel Yaskevich
>            Assignee: Pavel Yaskevich
>            Priority: Minor
>             Fix For: 1.1.7
>
>         Attachments: CASSANDRA-4937.patch
>
>
> After good amount of testing on one of the clusters it was found that in order to improve
read latency we need to minimize allocation rate that compression involves, that minimizes
GC (as well as heap usage) and substantially decreases latency on read heavy workloads. 
> I have also discovered that RAR skip cache harms performance in situation when reads
are done in parallel with compaction working with relatively big SSTable files (few GB and
more). The attached patch removes possibility to skip cache from compressed files (I can also
add changes to RAR to remove skip cache functionality as a separate patch). 

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