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From "Zhihong Yu (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5204) Backward compatibility fixes for 0.92
Date Mon, 16 Jan 2012 01:21:39 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5204?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13186641#comment-13186641
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Zhihong Yu commented on HBASE-5204:
-----------------------------------

+1 on the patches. 
Change in javadoc for patch 003 can be done at time of commit. 
                
> Backward compatibility fixes for 0.92
> -------------------------------------
>
>                 Key: HBASE-5204
>                 URL: https://issues.apache.org/jira/browse/HBASE-5204
>             Project: HBase
>          Issue Type: Bug
>          Components: ipc
>    Affects Versions: 0.92.0
>            Reporter: Benoit Sigoure
>            Assignee: Benoit Sigoure
>              Labels: backwards-compatibility
>         Attachments: 0001-Add-some-backward-compatible-support-for-reading-old.patch,
0002-Make-sure-that-a-connection-always-uses-a-protocol.patch, 0003-Change-the-code-used-when-serializing-HTableDescript.patch
>
>
> Attached are 3 patches that are necessary to allow compatibility between HBase 0.90.x
(and previous releases) and HBase 0.92.0.
> First of all, I'm well aware that 0.92.0 RC4 has been thumbed up by a lot of people and
would probably wind up being released as 0.92.0 tomorrow, so I sincerely apologize for creating
this issue so late in the process.  I spent a lot of time trying to work around the quirks
of 0.92 but once I realized that with a few very quasi-trivial changes compatibility would
be made significantly easier, I immediately sent these 3 patches to Stack, who suggested I
create this issue.
> The first patch is required as without it clients sending a 0.90-style RPC to a 0.92-style
server causes the server to die uncleanly.  It seems that 0.92 ships with {{\-XX:OnOutOfMemoryError="kill
\-9 %p"}}, and when a 0.92 server fails to deserialize a 0.90-style RPC, it attempts to allocate
a large buffer because it doesn't read fields of 0.90-style RPCs properly.  This allocation
attempt immediately triggers an OOME, which causes the JVM to die abruptly of a {{SIGKILL}}.
 So whenever a 0.90.x client attempts to connect to HBase, it kills whichever RS is hosting
the {{\-ROOT-}} region.
> The second patch fixes a bug introduced by HBASE-2002, which added support for letting
clients specify what "protocol" they want to speak.  If a client doesn't properly specify
what protocol to use, the connection's {{protocol}} field will be left {{null}}, which causes
any subsequent RPC on that connection to trigger an NPE in the server, even though the connection
was successfully established from the client's point of view.  The fix is to simply give the
connection a default protocol, by assuming the client meant to speak to a RegionServer.
> The third patch fixes an oversight that slipped in HBASE-451, where a change to {{HbaseObjectWritable}}
caused all the codes used to serialize {{Writables}} to shift by one.  This was carefully
avoided in other changes such as HBASE-1502, which cleanly removed entries for {{HMsg}} and
{{HMsg[]}}, so I don't think this breakage in HBASE-451 was intended.

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