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https://issues.apache.org/jira/browse/HBASE-7709?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13565847#comment-13565847
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Ian Varley commented on HBASE-7709:
-----------------------------------
Re: (B -> C -> B) -> A, that's fine; no participants are detecting a cycle
they're not part of (A isn't adding any peers, it's the slave). B detects a
cycle it's part of (B -> C -> B) and C does as well.
The API would be simple, and would let the caller walk the graph of clusters:
ask the peer you're trying to add for all of its peers, then ask each of them
in turn, and build up a graph structure that you can interrogate. Only call is
"Tell me your current peers".
I suppose this could cause problems if not all clusters can communicate; say,
if B is visible to A, and C is visible to B, but C is not visible to A. And I
guess there might be race conditions if you try to add peers on multiple
clusters simultaneously, there's not really a way to avoid that.
> 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
> Reporter: Lars Hofhansl
> Fix For: 0.96.0, 0.94.6
>
>
> 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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