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https://issues.apache.org/jira/browse/HBASE-7709?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13736423#comment-13736423
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Vasu Mariyala commented on HBASE-7709:
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[~jeffreyz]
The cluster ids in the WALEdit contains all the cluster ids including the
cluster id on which the entry was created first.When ReplicationSource runs on
A, it marks the cluster itself as consumed in the WALEdit. This entry would
then be sent on to B. ReplicationSource running on B checks that the cluster A
has already consumed and therefore does not send the entry back to A. If there
are any possible scenarios where this would not work, please do let me know.
> 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, 0.94.12
>
> Attachments: HBASE-7709.patch
>
>
> 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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