[
https://issues.apache.org/jira/browse/HDFS-6937?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15301723#comment-15301723
]
Yongjun Zhang commented on HDFS-6937:
-------------------------------------
I'm proposing a simplified solution here:
Instead of
{quote}
So intuitively, a solution would be, when downstream DN (DN3 here) found
checksum error, propagate this info back to upstream DN (DN2 here), DN2 checks
the correctness of the data already written to disk, and truncate the replica
to to MIN(correctDataSize, ACKedSize).
{quote}
what we can do is, when DN2 find DN3 failed, DN2 simply scan its own replica to
check possible corruption, if so, DN2 reports itself as the firstBadLink.
Thanks Colin for earlier discussion.
> Another issue in handling checksum errors in write pipeline
> -----------------------------------------------------------
>
> Key: HDFS-6937
> URL: https://issues.apache.org/jira/browse/HDFS-6937
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode, hdfs-client
> Affects Versions: 2.5.0
> Reporter: Yongjun Zhang
> Assignee: Colin Patrick McCabe
>
> Given a write pipeline:
> DN1 -> DN2 -> DN3
> DN3 detected cheksum error and terminate, DN2 truncates its replica to the
> ACKed size. Then a new pipeline is attempted as
> DN1 -> DN2 -> DN4
> DN4 detects checksum error again. Later when replaced DN4 with DN5 (and so
> on), it failed for the same reason. This led to the observation that DN2's
> data is corrupted.
> Found that the software currently truncates DN2's replca to the ACKed size
> after DN3 terminates. But it doesn't check the correctness of the data
> already written to disk.
> So intuitively, a solution would be, when downstream DN (DN3 here) found
> checksum error, propagate this info back to upstream DN (DN2 here), DN2
> checks the correctness of the data already written to disk, and truncate the
> replica to to MIN(correctDataSize, ACKedSize).
> Found this issue is similar to what was reported by HDFS-3875, and the
> truncation at DN2 was actually introduced as part of the HDFS-3875 solution.
> Filing this jira for the issue reported here. HDFS-3875 was filed by
> [~tlipcon]
> and found he proposed something similar there.
> {quote}
> if the tail node in the pipeline detects a checksum error, then it returns a
> special error code back up the pipeline indicating this (rather than just
> disconnecting)
> if a non-tail node receives this error code, then it immediately scans its
> own block on disk (from the beginning up through the last acked length). If
> it detects a corruption on its local copy, then it should assume that it is
> the faulty one, rather than the downstream neighbor. If it detects no
> corruption, then the faulty node is either the downstream mirror or the
> network link between the two, and the current behavior is reasonable.
> {quote}
> Thanks.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
