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From "Ariel Weisberg (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7404) Use direct i/o for sequential operations (compaction/streaming)
Date Tue, 30 Jun 2015 00:51:05 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7404?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14606758#comment-14606758
] 

Ariel Weisberg commented on CASSANDRA-7404:
-------------------------------------------

The patch will need to be rebased to be usable again. I can spend some time on that. The real
blocker is finding a way to demonstrate that this actually helps. I can help with rebasing
if there is interest in making this happen.

> 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.x
>
>
> 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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