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https://issues.apache.org/jira/browse/HDFS-6591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14045491#comment-14045491
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Liang Xie commented on HDFS-6591:
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bq. so it appears that we never copy to buf in this code path. I only see a
copy to buf inside the else path, when a hedged read actually happens. Did I
miss something?
Because in the if path, we passed this byte[] bb (ByteBuffer.wrap(buf, offset,
len)), it came from the original end-user input parameter. that's why we don't
need to do a explicit copy:)
bq. Let's set isHedgedRead = false in a JUnit After method instead of at the
end of individual methods.
seems you read "HDFS-6591.txt" patch, not "HDFS-6591-v2.txt" ?:) i had moved
it into a JUnit Before method per [~ajisakaa]'s suggestion, i assume it has a
similar effect like moving into a After method, right? Please correct me if i'm
wrong.
bq. Let's guarantee that output and input get closed. We can put the cleanup in
a finally block and call IOUtils#cleanup.
yes, let me do it in patch v3.
bq. Is it actually useful to add the new metric for HedgedReadOpsLoopNum
During debugging, i feel it's very convenient to catch/verify some unnecessary
loops, after a quick thinking, i didn't find any other easier choice to catch
such case. How about keeping it there. when we find it's a hotspot or this
feature is stable enough, then remove it ? (I can add a comment in v3 patch,
so we'll easy to recall those stuff)
> while loop is executed tens of thousands of times in Hedged Read
> ------------------------------------------------------------------
>
> Key: HDFS-6591
> URL: https://issues.apache.org/jira/browse/HDFS-6591
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs-client
> Affects Versions: 2.4.0
> Reporter: LiuLei
> Assignee: Liang Xie
> Attachments: HDFS-6591-v2.txt, HDFS-6591.txt,
> LoopTooManyTimesTestCase.patch
>
>
> I download hadoop-2.4.1-rc1 code from
> http://people.apache.org/~acmurthy/hadoop-2.4.1-rc1/, I test the Hedged
> Read. I find the while loop in hedgedFetchBlockByteRange method is executed
> tens of thousands of times.
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