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Date: Fri, 23 Jan 2009 02:27:02 -0800 (PST)
From: "dhruba borthakur (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Updated: (HADOOP-4379) In HDFS, sync() not yet guarantees
 data available to the new readers
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     [ https://issues.apache.org/jira/browse/HADOOP-4379?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

dhruba borthakur updated HADOOP-4379:
-------------------------------------

    Attachment: fsyncConcurrentReaders3.patch

This patch implements the following (as specified in the design doc for Appends, HADOOP-1700):
A reader checks to see if the file is being written to by another writer. if so, it fetches the size of the last block from the primary datanode. This does not have any performance impact for non-concurrent readers not does it have any impact on sync().

> In HDFS, sync() not yet guarantees data available to the new readers
> --------------------------------------------------------------------
>
>                 Key: HADOOP-4379
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4379
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: dfs
>            Reporter: Tsz Wo (Nicholas), SZE
>            Assignee: dhruba borthakur
>             Fix For: 0.19.1
>
>         Attachments: 4379_20081010TC3.java, fsyncConcurrentReaders.txt, fsyncConcurrentReaders3.patch, Reader.java, Writer.java
>
>
> In the append design doc (https://issues.apache.org/jira/secure/attachment/12370562/Appends.doc), it says
> * A reader is guaranteed to be able to read data that was 'flushed' before the reader opened the file
> However, this feature is not yet implemented.  Note that the operation 'flushed' is now called "sync".

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