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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-13047) S3a Forward seek in stream length to be configurable
Date Fri, 22 Apr 2016 13:37:12 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-13047?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15253934#comment-15253934
] 

Steve Loughran commented on HADOOP-13047:
-----------------------------------------

thanks. I'm doing the low-level metrics patch right now, even though the two patches address
different things, they wont merge cleanly.  Just a warning...

If you look at SwiftNativeInputStream, it reads ahead an arbitrary number of bytes; we could
do something like that

> S3a Forward seek in stream length to be configurable
> ----------------------------------------------------
>
>                 Key: HADOOP-13047
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13047
>             Project: Hadoop Common
>          Issue Type: Sub-task
>          Components: fs/s3
>    Affects Versions: 2.8.0
>            Reporter: Steve Loughran
>         Attachments: HADOOP-13047.WIP.patch
>
>
> Even with lazy seek, tests can show that sometimes a short-distance forward seek is triggering
a close + reopen, because the threshold for the seek is simply available bytes in the inner
stream.
> A configurable threshold would allow data to be read and discarded before that seek.
This should be beneficial over long-haul networks as the time to set up the TCP channel is
high, and TCP-slow-start means that the ramp up of bandwidth is slow. In such deployments,
it will better to read forward than re-open, though the exact "best" number will vary with
client and endpoint.



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