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https://issues.apache.org/jira/browse/HDFS-11160?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15710657#comment-15710657
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Yongjun Zhang commented on HDFS-11160:
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About your optimization:
{quote}
The basic idea is to copy the in-memory last partial chunk checksum in RBW
replica when converting an RBW to Finalized,
{quote}
I think for the bug reported here, what happened is
FinalizedReplica (S0) --> RBW (Append, S1) --> FinalizedReplica (S2)
The BlockSender constructor happens at S0, then an append happens, and go
through S1, S2, at S2, it updated the partial checksum on disk. Then
BlockSender starts reading the data and transfer data, and got an matching
checksum.
So I think your above optimization doesn't help this jira.
What do you think?
Thanks.
> VolumeScanner reports write-in-progress replicas as corrupt incorrectly
> -----------------------------------------------------------------------
>
> Key: HDFS-11160
> URL: https://issues.apache.org/jira/browse/HDFS-11160
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Environment: CDH5.7.4
> Reporter: Wei-Chiu Chuang
> Assignee: Wei-Chiu Chuang
> Attachments: HDFS-11160.001.patch, HDFS-11160.002.patch,
> HDFS-11160.003.patch, HDFS-11160.reproduce.patch
>
>
> Due to a race condition initially reported in HDFS-6804, VolumeScanner may
> erroneously detect good replicas as corrupt. This is serious because in some
> cases it results in data loss if all replicas are declared corrupt. This bug
> is especially prominent when there are a lot of append requests via
> HttpFs/WebHDFS.
> We are investigating an incidence that caused very high block corruption rate
> in a relatively small cluster. Initially, we thought HDFS-11056 is to blame.
> However, after applying HDFS-11056, we are still seeing VolumeScanner
> reporting corrupt replicas.
> It turns out that if a replica is being appended while VolumeScanner is
> scanning it, VolumeScanner may use the new checksum to compare against old
> data, causing checksum mismatch.
> I have a unit test to reproduce the error. Will attach later. A quick and
> simple fix is to hold FsDatasetImpl lock and read from disk the checksum.
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