[jira] [Resolved] (HDFS-16520) Improve EC pread: avoid potential reading whole block

["Wei-Chiu Chuang (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-16520?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wei-Chiu Chuang resolved HDFS-16520.
------------------------------------
    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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