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https://issues.apache.org/jira/browse/HDFS-2021?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13042208#comment-13042208
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Daryn Sharp commented on HDFS-2021:
-----------------------------------
I noticed that you omitted the conditional {{replyAck.isSuccess()}} when you
moved the code block that updates the {{bytesAcked}}. The {{isSuccess()}}
isn't tied to whether the ack was successfully sent upstream, but rather
whether the downstreams were all successful, thus is seems like the conditional
should be reinserted to preserve the current behavior. Changing the overall
logic seems fraught with peril...
That said, I'm a bit confused about why a datanode updates its {{bytesAcked}}
iff all downstreams are successful. The datanode received and wrote those
bytes so it seems like the conditional isn't needed in either case. Unless...
{{bytesAcked}} is intended to track exactly how many bytes were written
throughout the entire pipeline. I'd think that a pipeline should write as much
as it can even if downstreams are lost, then backfill the under-replicated
blocks. To satisfy curiosity, perhaps someone with more knowledge of the code
will comment.
> HDFS Junit test TestWriteRead failed with inconsistent visible length of a
> file
> --------------------------------------------------------------------------------
>
> Key: HDFS-2021
> URL: https://issues.apache.org/jira/browse/HDFS-2021
> Project: Hadoop HDFS
> Issue Type: Bug
> Environment: Linux RHEL5
> Reporter: CW Chung
> Assignee: John George
> Priority: Minor
> Attachments: HDFS-2021.patch
>
>
> The junit test failed when iterates a number of times with larger chunk size
> on Linux. Once a while, the visible number of bytes seen by a reader is
> slightly less than what was supposed to be.
> When run with the following parameter, it failed more often on Linux ( as
> reported by John George) than my Mac:
> private static final int WR_NTIMES = 300;
> private static final int WR_CHUNK_SIZE = 10000;
> Adding more debugging output to the source, this is a sample of the output:
> Caused by: java.io.IOException: readData mismatch in byte read:
> expected=2770000 ; got 2765312
> at
> org.apache.hadoop.hdfs.TestWriteRead.readData(TestWriteRead.java:141)
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