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From "vanessa (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7404) Use direct i/o for sequential operations (compaction/streaming)
Date Mon, 08 Dec 2014 02:15:13 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7404?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14237363#comment-14237363
] 

vanessa commented on CASSANDRA-7404:
------------------------------------

Hi ,why didn't  you  use direct I/O for write operation ?

> Use direct i/o for sequential operations (compaction/streaming)
> ---------------------------------------------------------------
>
>                 Key: CASSANDRA-7404
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7404
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jason Brown
>            Assignee: Ariel Weisberg
>              Labels: performance
>             Fix For: 3.0
>
>
> Investigate using linux's direct i/o for operations where we read sequentially through
a file (repair and bootstrap streaming, compaction reads, and so on). Direct i/o does not
go through the kernel page page, so it should leave the hot cache pages used for live reads
unaffected.
> Note: by using direct i/o, we will probably take a performance hit on reading the file
we're sequentially scanning through (that is, compactions may get slower), but the goal of
this ticket is to limit the impact of these background tasks on the main read/write functionality.
Of course, I'll measure any perf hit that is incurred, and see if there's any mechanisms to
mitigate it.



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