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https://issues.apache.org/jira/browse/HDFS-10182?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15213926#comment-15213926
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Walter Su commented on HDFS-10182:
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+1. I'll commit it shortly.
> Hedged read might overwrite user's buf
> --------------------------------------
>
> Key: HDFS-10182
> URL: https://issues.apache.org/jira/browse/HDFS-10182
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: zhouyingchao
> Assignee: zhouyingchao
> Attachments: HDFS-10182-001.patch
>
>
> In DFSInputStream::hedgedFetchBlockByteRange, during the first attempt, the
> passed-in buf from the caller is passed to another thread to fill. If the
> first attempt is timed out, the second attempt would be issued with another
> temp ByteBuffer. Now suppose the second attempt wins and the first attempt
> is blocked somewhere in the IO path. The second attempt's result would be
> copied to the buf provided by the caller and then caller would think the
> pread is all set. Later the caller might use the buf to do something else
> (for e.g. read another chunk of data), however, the first attempt in earlier
> hedgedFetchBlockByteRange might get some data and fill into the buf ...
> If this happens, the caller's buf would then be corrupted.
> To fix the issue, we should allocate a temp buf for the first attempt too.
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