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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-3672) Expose disk-location information for blocks to enable better scheduling
Date Thu, 26 Jul 2012 00:58:35 GMT

     [ https://issues.apache.org/jira/browse/HDFS-3672?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Andrew Wang updated HDFS-3672:
------------------------------

    Attachment: hdfs-3672-2.patch

Newer version of the patch, addressing Todd and Tom's comments.

One unfortunate bit is that to split the NN and DN RPCs, I needed to add a subclass of {{BlockLocation}}
that hides a corresponding {{LocatedBlock}}. An array of these {{HdfsBlockLocation}} is now
returned by {{DFS#getFileBlockLocations}}, and downcasted in {{DFSClient#getDiskBlockLocations}}
to retrieve the {{LocatedBlock}}.

I took Todd's advice about {{Integer.MAX_VALUE}} for denoting invalid blocks, but turn it
a boolean accessible via {{DiskId#isValid}} before it's shown to consumers of {{FileSystem}}.

Finally, I already renamed things to {{DiskBlockLocation}} based on Tom's comment, and reused
the name {{HdfsBlockLocation}} for my {{LocatedBlock}} wrapper class. I can re-rename both
of these if we don't like them.
                
> Expose disk-location information for blocks to enable better scheduling
> -----------------------------------------------------------------------
>
>                 Key: HDFS-3672
>                 URL: https://issues.apache.org/jira/browse/HDFS-3672
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 2.0.0-alpha
>            Reporter: Andrew Wang
>            Assignee: Andrew Wang
>         Attachments: hdfs-3672-1.patch, hdfs-3672-2.patch
>
>
> Currently, HDFS exposes on which datanodes a block resides, which allows clients to make
scheduling decisions for locality and load balancing. Extending this to also expose on which
disk on a datanode a block resides would enable even better scheduling, on a per-disk rather
than coarse per-datanode basis.
> This API would likely look similar to Filesystem#getFileBlockLocations, but also involve
a series of RPCs to the responsible datanodes to determine disk ids.

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