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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8430) Erasure coding: update DFSClient.getFileChecksum() logic for stripe files
Date Sun, 03 Jan 2016 17:44:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8430?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15080487#comment-15080487

Tsz Wo Nicholas Sze commented on HDFS-8430:

[~drankye], I think it is a good start for the first implementation.  We may improve it later
on.  Some ideas:
# Instead of sending all CRCs to the client, send all CRCs to one of the datanode in a block
group.  The datanode computes the block MD5s and returns them to the client.  Then, the computation
becomes distributed.
# We may consider changing the checksum algorithm for replicated files (although it is incompatible
with the old clusters)
## Use CRC64 (or some other linear code) for block checksum instead of MD5.  The datanode
may compute cell CRC64s and then send them to a client (or a datanode). We may combine the
cell CRC64s to obtain the block CRC64 since the code is linear.  Since datanodes send cell
checksums instead of data checksums, the network overhead becomes ignorable.
## Or simply compute cell checksums for replicated files instead of block checksums.

> Erasure coding: update DFSClient.getFileChecksum() logic for stripe files
> -------------------------------------------------------------------------
>                 Key: HDFS-8430
>                 URL: https://issues.apache.org/jira/browse/HDFS-8430
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>    Affects Versions: HDFS-7285
>            Reporter: Walter Su
>            Assignee: Kai Zheng
>         Attachments: HDFS-8430-poc1.patch
> HADOOP-3981 introduces a  distributed file checksum algorithm. It's designed for replicated
> {{DFSClient.getFileChecksum()}} need some updates, so it can work for striped block group.

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