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https://issues.apache.org/jira/browse/HDFS-16520?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Wei-Chiu Chuang resolved HDFS-16520.
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Resolution: Fixed
Merged the PR and cherrypicked into branch-3.3.
Thanks!
> Improve EC pread: avoid potential reading whole block
> -----------------------------------------------------
>
> Key: HDFS-16520
> URL: https://issues.apache.org/jira/browse/HDFS-16520
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: dfsclient, ec, erasure-coding
> Affects Versions: 3.3.1, 3.3.2
> Reporter: daimin
> Assignee: daimin
> Priority: Major
> Labels: pull-request-available
> Fix For: 3.4.0, 3.3.4
>
> Time Spent: 4h 20m
> Remaining Estimate: 0h
>
> HDFS client 'pread' represents 'position read', this kind of read just need a
> range of data instead of reading the whole file/block. By using
> BlockReaderFactory#setLength, client tells datanode the block length to be
> read from disk and sent to client.
> To EC file, the block length to read is not well set, by default using
> 'block.getBlockSize() - offsetInBlock' to both pread and sread. Thus datanode
> read much more data and send to client, and abort when client closes
> connection. There is a lot waste of resource to this situation.
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