[jira] [Commented] (CASSANDRA-6890) Standardize on a single read path

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

    [ https://issues.apache.org/jira/browse/CASSANDRA-6890?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14026475#comment-14026475 ] 

Jason Brown commented on CASSANDRA-6890:
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Hmm, are we sure we really want to do this before CASSANDRA-5863 is proven (or even implemented)? The v1 patch is simple enough, but we are taking a known performance hit against an unknown future payoff. How much simpler would removing the mmap path make implementing CASSANDRA-5863? I can't imagine it'd make that much of a difference?

Furthermore, if anyone is truly interested, I'll be talking about direct i/o (O_DIRECT) at the 2014 NGCC. 

> Standardize on a single read path
> ---------------------------------
>
>                 Key: CASSANDRA-6890
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6890
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Joshua McKenzie
>            Assignee: Joshua McKenzie
>              Labels: performance
>             Fix For: 3.0
>
>         Attachments: 6890_v1.txt, mmap_gc.jpg, mmap_jstat.txt, mmap_perf.txt, nommap_gc.jpg, nommap_jstat.txt
>
>
> Since we actively unmap unreferenced SSTR's and also copy data out of those readers on the read path, the current memory mapped i/o is a lot of complexity for very little payoff.  Clean out the mmapp'ed i/o on the read path.



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