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From "Zhe Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9576) HTrace: collect position/length information on read operations
Date Thu, 14 Jan 2016 19:45:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9576?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15098719#comment-15098719
] 

Zhe Zhang commented on HDFS-9576:
---------------------------------

Thanks for the review Colin.

bq. Can we use "pos" instead?
Good point. Will update in next rev.

Tracing the "requested length" is mostly for profiling application behavior. I agree that
the "returned length" is what ultimately matters in the particular scenario being traced.
But "requested length" gives insights on what-if analysis -- e.g. a different system could
return more data and fully satisfy the request.

So how about only reporting "returned length" if it's different from requested?

> HTrace: collect position/length information on read operations
> --------------------------------------------------------------
>
>                 Key: HDFS-9576
>                 URL: https://issues.apache.org/jira/browse/HDFS-9576
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client, tracing
>    Affects Versions: 2.7.1
>            Reporter: Zhe Zhang
>            Assignee: Zhe Zhang
>         Attachments: HDFS-9576.00.patch, HDFS-9576.01.patch, HDFS-9576.02.patch, HDFS-9576.03.patch,
HDFS-9576.04.patch, HDFS-9576.05.patch
>
>
> HTrace currently collects the path of each read operation (both stateful and position
reads). To better understand applications' I/O behavior, it is also useful to track the position
and length of read operations.



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