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https://issues.apache.org/jira/browse/HDFS-1798?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Matt Foley updated HDFS-1798:
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Attachment: 1798_asyncSaveNamespace_v1.patch
This is a preliminary upload for design review. Still working on the unit
tests. Patch contains the following:
* FSNamesystem
** added ability to place "hold" on Safe Mode
** also fixed several left-over uses of "synchronized" instead of read/write
lock
* FSImage - created async thread to run saveNamespace(), guarded by a hold on
Safe Mode.
* FSDirectory - loadFSImage() now calls asyncSaveNamespace() instead of
saveNamespace().
It would have been very difficult to restructure FSDirectory.loadFSImage() to
split into separate read and write phases, as initially proposed. Instead, I
provided a lenient initializer for startup safe mode, initializeSafeMode(). It
is called from both asyncSaveNamespace() and FSNamesystem.initialize(), and
handles the possible combinations of events correctly.
> saveNamespace should background the writing of the FSImage files when in
> SafeMode
> ---------------------------------------------------------------------------------
>
> Key: HDFS-1798
> URL: https://issues.apache.org/jira/browse/HDFS-1798
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Matt Foley
> Assignee: Matt Foley
> Attachments: 1798_asyncSaveNamespace_v1.patch
>
>
> Even with parallel writes of the FSImage files (HDFS-1071), large clusters
> still typically spend 5 minutes writing the files. When in SafeMode, it
> should be safe to background these writes instead of waiting for them. To
> enable this, the namenode must be prevented from leaving SafeMode until the
> writes are done.
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