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https://issues.apache.org/jira/browse/HDFS-11160?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15749130#comment-15749130
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Xiao Chen commented on HDFS-11160:
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I was pinged to review this as well. Change makes sense to me, verified test
fails without the BlockSender change.
Test appears to have some duplicate code (wait for scan, and verify info), +1
after that's cleaned up.
Nice work here Wei-Chiu! Also thanks Yongjun and Kihwal for the reviews.
> 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-11160.004.patch, HDFS-11160.005.patch,
> HDFS-11160.006.patch, HDFS-11160.branch-2.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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