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From "Gregory Chanan (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-6710) 0.92/0.94 compatibility issues due to HBASE-5206
Date Sat, 01 Sep 2012 04:27:07 GMT
Gregory Chanan created HBASE-6710:
-------------------------------------

             Summary: 0.92/0.94 compatibility issues due to HBASE-5206
                 Key: HBASE-6710
                 URL: https://issues.apache.org/jira/browse/HBASE-6710
             Project: HBase
          Issue Type: Bug
            Reporter: Gregory Chanan
            Assignee: Gregory Chanan
            Priority: Critical
             Fix For: 0.94.2


HBASE-5206 introduces some compatibility issues between {0.94,0.94.1} and
{0.92.0,0.92.1}.  The release notes of HBASE-5155 describes the issue (HBASE-5206 is a backport
of HBASE-5155).

I think we can make 0.94.2 compatible with both {0.94.0,0.94.1} and {0.92.0,0.92.1}, although
one of those sets will require configuration changes.

The basic problem is that there is a znode for each table "zookeeper.znode.tableEnableDisable"
that is handled differently.

On 0.92.0 and 0.92.1 the states for this table are:
[ disabled, disabling, enabling ] or deleted if the table is enabled

On 0.94.1 and 0.94.2 the states for this table are:
[ disabled, disabling, enabling, enabled ]

What saves us is that the location of this znode is configurable.  So the basic idea is to
have the 0.94.2 master write two different znodes, "zookeeper.znode.tableEnableDisabled92"
and "zookeeper.znode.tableEnableDisabled94" where the 92 node is in 92 format, the 94 node
is in 94 format.  And internally, the master would only use the 94 format in order to solve
the original bug HBASE-5155 solves.
We can of course make one of these the same default as exists now, so we don't need to make
config changes for one of 0.92 or 0.94 clients.  I argue that 0.92 clients shouldn't have
to make config changes for the same reason I argued above.  But that is debatable.

Then, I think the only question left is the question of how to bring along the {0.94.0, 0.94.1}
crew.  A {0.94.0, 0.94.1} client would work against a 0.94.2 cluster by just configuring "zookeeper.znode.tableEnableDisable"
in the client to be whatever "zookeeper.znode.tableEnableDisabled94" is in the cluster.  A
0.94.2 client would work against both a {0.94.0, 0.94.1} and {0.92.0, 0.92.1} cluster if it
had HBASE-6268 applied.  About rolling upgrade from {0.94.0, 0.94.1} to 0.94.2 -- I'd have
to think about that.  Do the regionservers ever read the tableEnableDisabled znode?

On the mailing list, Lars H suggested the following:
"The only input I'd have is that format we'll use going forward will not have a version attached
to it.
So maybe the 92 version would still be called "zookeeper.znode.tableEnableDisable" and the
new node could have a different name "zookeeper.znode.tableEnableDisableNew" (or something)."

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