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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-2195) Support cyclic replication
Date Mon, 05 Sep 2011 19:02:12 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13097253#comment-13097253
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Lars Hofhansl commented on HBASE-2195:
--------------------------------------

@Ted
re HLogKey: Correct, it does not extend VersionWritable. This way I can make sure that 0.92
can read all log files that 0.90.x could read (currently 0.90.x might fail on earlier log
files, but that damage is already done)
If we're not concerned about this, I agree using VersionedWritable is better.

re  byte cluster id to UUID: What I am saying is that *we do not need a mapping*. A replication
source used some random numbering scheme (that we can change at any given time). When the
log is replicated it is tagged the correct UUID. And as an *optimization* a source also retrieves
the sink's cluster UUID via ZK to avoid shipping logs if not needed.
With some restructuring (that I don't think should go into 0.92), the byte cluster id can
just go away. That involves backwards compatibility needs in how to read existing ZNode entries
and rethinking how a replication source would maintain its sink(s).

re readByteArray: I think I am missing something. As the old logs can have any byte combination
at the beginning, we'll always potentially run into problems. So either we break compatibility

once to start using VersionedWritable now, or use the former cluster id byte going forward
and that would provide backwards compatibility in 0.92.


> Support cyclic replication
> --------------------------
>
>                 Key: HBASE-2195
>                 URL: https://issues.apache.org/jira/browse/HBASE-2195
>             Project: HBase
>          Issue Type: Sub-task
>          Components: replication
>            Reporter: Jean-Daniel Cryans
>         Attachments: 2195-v5.txt, 2195.txt
>
>
> We need to support cyclic replication by using the cluster id of each HlogKey and stop
replicating when it goes back to the original cluster.

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