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https://issues.apache.org/jira/browse/HDFS-3721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13422575#comment-13422575
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Todd Lipcon commented on HDFS-3721:
-----------------------------------
bq. Todd, I will review this in a couple of days. Looking at the issue briefly,
this is only an issue with DataTransferProtocol, due to packet header length.
It should not happen in RPC right? I would be good to review RPC code once more
to confirm it.
I think RPC is basically sound. I've done diffs of the protobufs between trunk
and 2.0 and all the changes look compatible. This was just a special case
because, when I did the original PB-ification, I took the simpler route of
maintaining fixed-length headers. Then I overlooked the bit of HDFS-744 which
made the header non-fixed-width (oops).
bq. In a related note, we should think about what backward/forward
compatibility for an alpha release means and how to handle it when we find
issues.
In that case, I'd also like to consider whether we can promote the HDFS side of
2.0.x to "beta". We've seen very few issues after extensive testing. I don't
want the alpha state of MR2 to hold back stability classification of HDFS,
which is important for those users who aren't using MR2. But that's probably
better suited for a mailing list discussion.
> hsync support broke wire compatibility
> --------------------------------------
>
> Key: HDFS-3721
> URL: https://issues.apache.org/jira/browse/HDFS-3721
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: data-node, hdfs client
> Affects Versions: 2.1.0-alpha
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Priority: Critical
> Attachments: hdfs-3721.txt
>
>
> HDFS-744 added support for hsync to the data transfer wire protocol. However,
> it actually broke wire compatibility: if the client has hsync support but the
> server does not, the client cannot read or write data on the old cluster.
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