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From "Jonathan Park (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-2668) slow WAL writes
Date Tue, 15 Apr 2014 16:42:16 GMT


Jonathan Park commented on ACCUMULO-2668:

Hey Sean. It would be great to be listed as a contributor.

Name: Jonathan Park
Company name: sqrrl
Timezone: ET

Thanks for all the help everyone! 

> slow WAL writes
> ---------------
>                 Key: ACCUMULO-2668
>                 URL:
>             Project: Accumulo
>          Issue Type: Bug
>    Affects Versions: 1.6.0
>            Reporter: Jonathan Park
>            Assignee: Jonathan Park
>            Priority: Blocker
>              Labels: 16_qa_bug
>             Fix For: 1.6.1
>         Attachments: ACCUMULO-2668.0.patch.txt, 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 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 implementation that I don't believe can be satisfied
(line 384).

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