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https://issues.apache.org/jira/browse/HDFS-3672?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andrew Wang updated HDFS-3672:
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Attachment: hdfs-3672-1.patch
First hack at this. I still want to add some more tests, but I think the design
is about right.
This essentially provides the same API as {{DFS#getFileBlockLocations}}, except
it returns a subclass of {{BlockLocation}}, {{HdfsBlockLocation}}, which has an
additional array of {{byte}}s which is an opaque identifier that specifies on
which disk on a datanode the block resides.
Currently, this ID is mapped to the index of the HDFS data directory containing
the block file (e.g. /data/1, /data/2). This can thus change across
reboots/config changes, and clients need to be prepared to requery anyway since
blocks do move around as part of normal operation.
I'd like to perhaps split the new {{DFS#getFileHdfsBlockLocations}} function
into a call to {{DFS#getFileBlockLocations}} to do the NN query to get block
locations, and then pass these to some other call ({{DFS#getDiskIds}}?), since
this would let you do multiple calls to {{DFS#getFileBlockLocations}} and then
do one series of RPCs to the datanodes. But, I need to figure out how to change
the {{BlockLocation[]}} back into a {{LocatedBlock[]}}.
It might also be nice to do the DN RPCs in parallel, since right now it's
serial setup, query, teardown for each DN.
> 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
>
>
> 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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