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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4379) In HDFS, sync() not yet guarantees data available to the new readers
Date Tue, 19 May 2009 00:22:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4379?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12710555#action_12710555
] 

Hairong Kuang commented on HADOOP-4379:
---------------------------------------

If one of the datanodes in the pipeline has a very very slow disk, it is possible that when
sync returns, not all the syned data get flushed to the disk yet. If this datanode dies and
restarts before the lease recovery starts, I think the lease recovery will remove the synced
data.

> 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
>            Priority: Blocker
>             Fix For: 0.19.2
>
>         Attachments: 4379_20081010TC3.java, fsyncConcurrentReaders.txt, fsyncConcurrentReaders3.patch,
fsyncConcurrentReaders4.patch, fsyncConcurrentReaders5.txt, fsyncConcurrentReaders6.patch,
fsyncConcurrentReaders9.patch, hypertable-namenode.log.gz, namenode.log, namenode.log, Reader.java,
Reader.java, reopen_test.sh, ReopenProblem.java, Writer.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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