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From "Ted Yu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6710) 0.92/0.94 compatibility issues due to HBASE-5206
Date Fri, 14 Sep 2012 16:34:07 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6710?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13455919#comment-13455919

Ted Yu commented on HBASE-6710:

I was trying to wrap up 0.92.2 release. So pardon me for late comments.

Looking at code for void setTableState(final String tableName, final TableState state):
      if (settingToEnabled) {
        ZKUtil.deleteNodeFailSilent(this.watcher, znode92);
Should we fail silently if node deletion fails ? Would this increase the chance of inconsistency
between znode92 and znode ?

Should hbck be enhanced to detect / fix such inconsistencies ?
> 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
>         Attachments: HBASE-6710-v3.patch
> 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
> 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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