Mailing-List: contact core-dev-help@hadoop.apache.org; run by ezmlm
Precedence: bulk
Reply-To: core-dev@hadoop.apache.org
Message-ID: <15159883.1202944629095.JavaMail.jira@brutus>
Date: Wed, 13 Feb 2008 15:17:09 -0800 (PST)
From: "Raghu Angadi (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-1702) Reduce buffer copies when data is
 written to DFS
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit


    [ https://issues.apache.org/jira/browse/HADOOP-1702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12568748#action_12568748 ] 

Raghu Angadi commented on HADOOP-1702:
--------------------------------------

The protocol and code has changed quite a bit around write path, but memory copies essentially remain the same as in the picture above.

> Reduce buffer copies when data is written to DFS
> ------------------------------------------------
>
>                 Key: HADOOP-1702
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1702
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.14.0
>            Reporter: Raghu Angadi
>            Assignee: Raghu Angadi
>             Fix For: 0.17.0
>
>
> HADOOP-1649 adds extra buffering to improve write performance.  The following diagram shows buffers as pointed by (numbers). Each eatra buffer adds an extra copy since most of our read()/write()s match the io.bytes.per.checksum, which is much smaller than buffer size.
> {noformat}
>        (1)                 (2)          (3)                 (5)
>    +---||----[ CLIENT ]---||----<>-----||---[ DATANODE ]---||--<>-> to Mirror  
>    | (buffer)                  (socket)           |  (4)
>    |                                              +--||--+
>  =====                                                    |
>  =====                                                  =====
>  (disk)                                                 =====
> {noformat}
> Currently loops that read and write block data, handle one checksum chunk at a time. By reading multiple chunks at a time, we can remove buffers (1), (2), (3), and (5). 
> Similarly some copies can be reduced when clients read data from the DFS.

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.