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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5698) Use protobuf to serialize / deserialize FSImage
Date Mon, 30 Dec 2013 20:51:51 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5698?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13859071#comment-13859071
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Andrew Wang commented on HDFS-5698:
-----------------------------------

+1, I'd really like to see this in 3.0. It'd be great if we could protobuf the edits as well,
since that code is flawed for the same reasons as above.

> Use protobuf to serialize / deserialize FSImage
> -----------------------------------------------
>
>                 Key: HDFS-5698
>                 URL: https://issues.apache.org/jira/browse/HDFS-5698
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Haohui Mai
>            Assignee: Haohui Mai
>
> Currently, the code serializes FSImage using in-house serialization mechanisms. There
are a couple disadvantages of the current approach:
> # Mixing the responsibility of reconstruction and serialization / deserialization. The
current code paths of serialization / deserialization have spent a lot of effort on maintaining
compatibility. What is worse is that they are mixed with the complex logic of reconstructing
the namespace, making the code difficult to follow.
> # Poor documentation of the current FSImage format. The format of the FSImage is practically
defined by the implementation. An bug in implementation means a bug in the specification.
Furthermore, it also makes writing third-party tools quite difficult.
> # Changing schemas is non-trivial. Adding a field in FSImage requires bumping the layout
version every time. Bumping out layout version requires (1) the users to explicitly upgrade
the clusters, and (2) putting new code to maintain backward compatibility.
> This jira proposes to use protobuf to serialize the FSImage. Protobuf has been used to
serialize / deserialize the RPC message in Hadoop.
> Protobuf addresses all the above problems. It clearly separates the responsibility of
serialization and reconstructing the namespace. The protobuf files document the current format
of the FSImage. The developers now can add optional fields with ease, since the old code can
always read the new FSImage.



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