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https://issues.apache.org/jira/browse/HDFS-4677?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ivan Mitic updated HDFS-4677:
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Attachment: HDFS-4677.2.patch
Attaching the updated patch with the following changes:
- Addressing Chris' feedback to pass the Configuration object from FSEditLog
down to EditLogFileOutputStream
- Changing the new config name
One thing that bothers me in the latest patch is now having two constructors
for FileJournalManager and EditLogFileOutputStream, one with conf and one
without. Given that the one with conf is the right choice for most cases, it
might make sense to lose the other one. However, making this change would
further increase the scope of this simple Jira, so I’m deferring this question
to the community.
> Editlog should support synchronous writes
> -----------------------------------------
>
> Key: HDFS-4677
> URL: https://issues.apache.org/jira/browse/HDFS-4677
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 3.0.0, 1-win
> Reporter: Ivan Mitic
> Assignee: Ivan Mitic
> Attachments: HDFS-4677.2.patch, HDFS-4677.patch
>
>
> In the current implementation, NameNode editlog performs syncs to the
> persistent storage using the {{FileChannel#force}} Java APIs. This API is
> documented to be slower compared to an alternative where {{RandomAccessFile}}
> is opened with "rws" flags (synchronous writes).
> We instrumented {{FileChannel#force}} on Windows and it some
> software/hardware configurations it can perform significantly slower than the
> “rws” alternative.
> In terms of the Windows APIs, FileChannel#force internally calls
> [FlushFileBuffers|http://msdn.microsoft.com/en-us/library/windows/desktop/aa364439(v=vs.85).aspx]
> while RandomAccessFile (“rws”) opens the file with the
> [FILE_FLAG_WRITE_THROUGH flag|http://support.microsoft.com/kb/99794].
> With this Jira I'd like to introduce a flag that provide means to configure
> NameNode to use synchronous writes. There is a catch though, the behavior of
> the "rws" flags is platform and hardware specific and might not provide the
> same level of guarantees as {{FileChannel#force}} w.r.t. flushing the on-disk
> cache. This is an expert level setting, and it should be documented as such.
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