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From "Jeffrey Zhong (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7709) Infinite loop possible in Master/Master replication
Date Wed, 17 Jul 2013 02:32:52 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7709?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13710629#comment-13710629
] 

Jeffrey Zhong commented on HBASE-7709:
--------------------------------------

For 0.94, I think it'd be better that we introduce a configuration setting "hbase.replication.reset.clusterid=<clusterId
which a user specifies>". Only cluster specified here reset clusterId to itself so that
we still can support master-master replication involving more than 2 nodes without bumping
up logkey version.

We could possibly bump up HLogKey version with one upgrade configuration setting like "upgrade.logkey"
plus two rounds of rolling restart. Originally we set the config setting to false. First round
rolling start to upgrade RS bits(new RS still write hlogkey in old version) and after all
RS upgraded, we set the configuration to true and then second rolling start.

The above complicates the upgrade scenario a little bit and requires all involved clusters
in the replication are upgraded. 

                
> Infinite loop possible in Master/Master replication
> ---------------------------------------------------
>
>                 Key: HBASE-7709
>                 URL: https://issues.apache.org/jira/browse/HBASE-7709
>             Project: HBase
>          Issue Type: Bug
>          Components: Replication
>    Affects Versions: 0.94.6, 0.95.1
>            Reporter: Lars Hofhansl
>             Fix For: 0.98.0, 0.95.2, 0.94.10
>
>
>  We just discovered the following scenario:
> # Cluster A and B are setup in master/master replication
> # By accident we had Cluster C replicate to Cluster A.
> Now all edit originating from C will be bouncing between A and B. Forever!
> The reason is that when the edit come in from C the cluster ID is already set and won't
be reset.
> We have a couple of options here:
> # Optionally only support master/master (not cycles of more than two clusters). In that
case we can always reset the cluster ID in the ReplicationSource. That means that now cycles
> 2 will have the data cycle forever. This is the only option that requires no changes
in the HLog format.
> # Instead of a single cluster id per edit maintain a (unordered) set of cluster id that
have seen this edit. Then in ReplicationSource we drop any edit that the sink has seen already.
The is the cleanest approach, but it might need a lot of data stored per edit if there are
many clusters involved.
> # Maintain a configurable counter of the maximum cycle side we want to support. Could
default to 10 (even maybe even just). Store a hop-count in the WAL and the ReplicationSource
increases that hop-count on each hop. If we're over the max, just drop the edit.

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