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https://issues.apache.org/jira/browse/HDFS-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15189771#comment-15189771
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stack commented on HDFS-3702:
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Excellent. +1.
Below are nits for if you make a new version of the patch:
Be more forthright in the doc on NO_LOCAL_WRITE. Change "Advice the block not
being written to the local DataNode which is on the same host as the client."
to "Advise that a block replica NOT be written to the local DataNode where
'local' means the same host as the client is being run on."
I suppose there has to be two declarations of the enum NO_LOCAL_WRITE; i.e. we
have to do the convertion from CreateFlag. NO_LOCAL_WRITE to AddBlockFlag.
NO_LOCAL_WRITE
The protected EnumSet<AddBlockFlag> addBlockFlags() { method is an accessor?
Should it be called getAddBlockFlags?
Whats happening here:
{code}
255 if (!avoidLocalNode || results.size() < numOfReplicas) {
256 LOG.debug("Fallback to use the default block placement.");
{code}
If < numOfReplicas we will start writing local? Add this to release note I'd
say.
> Add an option for NOT writing the blocks locally if there is a datanode on
> the same box as the client
> -----------------------------------------------------------------------------------------------------
>
> Key: HDFS-3702
> URL: https://issues.apache.org/jira/browse/HDFS-3702
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client
> Affects Versions: 2.5.1
> Reporter: Nicolas Liochon
> Assignee: Lei (Eddy) Xu
> Priority: Minor
> Labels: BB2015-05-TBR
> Attachments: HDFS-3702.000.patch, HDFS-3702.001.patch,
> HDFS-3702.002.patch, HDFS-3702.003.patch, HDFS-3702.004.patch,
> HDFS-3702.005.patch, HDFS-3702.006.patch, HDFS-3702.007.patch
>
>
> This is useful for Write-Ahead-Logs: these files are writen for recovery
> only, and are not read when there are no failures.
> Taking HBase as an example, these files will be read only if the process that
> wrote them (the 'HBase regionserver') dies. This will likely come from a
> hardware failure, hence the corresponding datanode will be dead as well. So
> we're writing 3 replicas, but in reality only 2 of them are really useful.
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