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https://issues.apache.org/jira/browse/HDFS-11187?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16360202#comment-16360202
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Wei-Chiu Chuang commented on HDFS-11187:
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Regarding the rev002 of the branch-2 patch – the code in
{{FsVolumeImpl#addFinalizedBlock()}} meant to copy the in-memory checksum of
rbw replica to the in-memory checksum of finalized replica. Your patch forces
the finalized replica to load checksum from disk and that could cause extra
disk access.
> Optimize disk access for last partial chunk checksum of Finalized replica
> -------------------------------------------------------------------------
>
> Key: HDFS-11187
> URL: https://issues.apache.org/jira/browse/HDFS-11187
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Reporter: Wei-Chiu Chuang
> Assignee: Gabor Bota
> Priority: Major
> Fix For: 3.1.0, 3.0.2
>
> Attachments: HDFS-11187-branch-2.001.patch,
> HDFS-11187-branch-2.002.patch, HDFS-11187.001.patch, HDFS-11187.002.patch,
> HDFS-11187.003.patch, HDFS-11187.004.patch, HDFS-11187.005.patch
>
>
> The patch at HDFS-11160 ensures BlockSender reads the correct version of
> metafile when there are concurrent writers.
> However, the implementation is not optimal, because it must always read the
> last partial chunk checksum from disk while holding FsDatasetImpl lock for
> every reader. It is possible to optimize this by keeping an up-to-date
> version of last partial checksum in-memory and reduce disk access.
> I am separating the optimization into a new jira, because maintaining the
> state of in-memory checksum requires a lot more work.
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