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Date: Mon, 14 Apr 2014 19:11:15 +0000 (UTC)
From: "Josh Elser (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (ACCUMULO-2668) slow WAL writes
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    [ https://issues.apache.org/jira/browse/ACCUMULO-2668?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13968694#comment-13968694 ] 

Josh Elser commented on ACCUMULO-2668:
--------------------------------------

(re-comment from IRC)

I was just looking into some performance decreases on 1.6.0-rc1. I'll apply this and poke at it. Thanks again for the patch.

> slow WAL writes
> ---------------
>
>                 Key: ACCUMULO-2668
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-2668
>             Project: Accumulo
>          Issue Type: Bug
>    Affects Versions: 1.6.0
>            Reporter: Jonathan Park
>              Labels: 16_qa_bug
>         Attachments: noflush.diff
>
>
> During continuous ingest, we saw over 70% of our ingest time taken up by writes to the WAL. When we ran the DfsLogger in isolation (created one outside of the Tserver), we saw about ~25MB/s throughput as opposed to nearly 100MB/s from just writing directly to an hdfs outputstream (computed by taking the estimated size of the mutations sent to the DfsLogger class divided by the time it took for it to flush + sync the data to HDFS).
> After investigating, we found one possible culprit was the NoFlushOutputStream. It is a subclass of java.io.FilterOutputStream but does not override the write(byte[], int, int) method signature. The javadoc indicates that subclasses of the FilterOutputStream should provide a more efficient implementation.
> I've attached a small diff that illustrates and addresses the issue but this may not be how we ultimately want to fix it.
> As a side note, I may be misreading the implementation of DfsLogger, but it looks like we always make use of the NoFlushOutputStream, even if encryption isn't enabled. There appears to be a faulty check in the DfsLogger.open() implementation that I don't believe can be satisfied (line 384).


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