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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8088) Reduce the number of HTrace spans generated by HDFS reads
Date Thu, 09 Apr 2015 17:55:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8088?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14487757#comment-14487757

Colin Patrick McCabe commented on HDFS-8088:

Thanks for looking at this.

bq. Colin, thanks for working on this, I have not gone through HDFS-8069, does it really degrade
the performance of DFSInputStream a lot? If so, I think this is a block issue and let's make
it in ASAP.

It doesn't degrade the performance at all if tracing is turned off.

bq. \[The change to hedgedReadId\] is not necessary.

True, but I think it's more intuitive to start the count at 1 than 0.  Just for some background,
{{hedgedReadId}} is something I introduced, and which is only used for tracing.

> Reduce the number of HTrace spans generated by HDFS reads
> ---------------------------------------------------------
>                 Key: HDFS-8088
>                 URL: https://issues.apache.org/jira/browse/HDFS-8088
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Colin Patrick McCabe
>            Assignee: Colin Patrick McCabe
>         Attachments: HDFS-8088.001.patch
> HDFS generates too many trace spans on read right now.  Every call to read() we make
generates its own span, which is not very practical for things like HBase or Accumulo that
do many such reads as part of a single operation.  Instead of tracing every call to read(),
we should only trace the cases where we refill the buffer inside a BlockReader.

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