[jira] Commented: (HADOOP-6307) Support reading on un-closed SequenceFile

["Hong Tang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-6307?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12764276#action_12764276 ] 

Hong Tang commented on HADOOP-6307:
-----------------------------------

Not sure why this issue only hits SequenceFile. The problem applies equally to TFile (although this was pushed to the caller).

I have previously asked around why we cannot do "seek(Long.MAX_VALUE); return getPos();" to determine the length of the file, and I was told that you could actually seek beyond the end of the file. TRUE or FALSE?

Another question is why we cannot support seek like POSIX does, where we can seek in relation to the {begin,current,end} position of the file?

> Support reading on un-closed SequenceFile
> -----------------------------------------
>
>                 Key: HADOOP-6307
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6307
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: io
>            Reporter: Tsz Wo (Nicholas), SZE
>
> When a SequenceFile.Reader is constructed, it calls fs.getFileStatus(file).getLen().  However, fs.getFileStatus(file).getLen() does not return the hflushed length for un-closed file since the Namenode does not know the hflushed length.  DFSClient have to ask a datanode for the length last block which is being written; see also HDFS-570.

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