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Date: Tue, 22 May 2012 17:14:41 +0000 (UTC)
From: "Eric Newton (JIRA)" <jira@apache.org>
To: dev@accumulo.apache.org
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Subject: [jira] [Commented] (ACCUMULO-578) consider using hdfs for the walog
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    [ https://issues.apache.org/jira/browse/ACCUMULO-578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13281103#comment-13281103 ] 

Eric Newton commented on ACCUMULO-578:
--------------------------------------

Todd, preliminary testing shows a considerable improvement interleaving writes with flushes.

|Logger rate|~432K|
|HDFS rate|~487K|
|HDFS with parallel flush|~699K|


> consider using hdfs for the walog
> ---------------------------------
>
>                 Key: ACCUMULO-578
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-578
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: logger, tserver
>    Affects Versions: 1.5.0-SNAPSHOT
>            Reporter: Eric Newton
>            Assignee: Eric Newton
>         Attachments: HDFS_WAL_states.pdf, NNOpsComparison.pdf, comparison.png
>
>
> Using HDFS for walogs would fix:
>  * ACCUMULO-84: any node can read the replicated files
>  * ACCUMULO-558: wouldn't need to monitor loggers
>  * ACCUMULO-544: log references wouldn't include hostnames
>  * ACCUMULO-423: wouldn't need to monitor loggers
>  * ACCUMULO-258: hdfs has load balancing already
> To implement it, we would need the ability to distribute log sorts.
> Continuing to use loggers helps us avoid:
>  * hdfs pipeline strategy
>  * we don't have fine-grained insight when a single node makes dfs slow
>  * additional namenode pressure
>  * flexibility: for example, we can add fadvise() calls to the logger before HDFS supports it

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