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https://issues.apache.org/jira/browse/HADOOP-13047?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15256525#comment-15256525
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Steve Loughran commented on HADOOP-13047:
-----------------------------------------
HADOOP-13028 has an attachment which compares read bandwidths to open
time...from the numbers locally to the US, I'm seeing a forward skip of < 800K
would be faster than closing and reopening the connection —and that's ignoring
the effects of TCP slow start on followon reads
{code}
2016-04-25 17:01:09,584 INFO scale.S3AScaleTestBase
(S3AScaleTestBase.java:end(181)) - Duration of Open stream: 164,965,000 nS
2016-04-25 17:01:13,613 INFO scale.S3AScaleTestBase
(S3AScaleTestBase.java:end(181)) - Duration of Time to read 20405780 bytes:
4,029,203,000 nS
2016-04-25 17:01:13,614 INFO scale.TestS3AInputStreamPerformance
(TestS3AInputStreamPerformance.java:bandwidth(135)) - Bandwidth = 5.064471 MB/S
2016-04-25 17:01:13,614 INFO scale.TestS3AInputStreamPerformance
(TestS3AInputStreamPerformance.java:testTimeToOpenAndReadWholeFileByByte(97)) -
An open() call has the equivalent duration of reading 837,385 bytes
{code}
> 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.2.patch, 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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