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https://issues.apache.org/jira/browse/HBASE-7709?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13738999#comment-13738999
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Dave Latham commented on HBASE-7709:
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Thanks all for the great work on this.
We currently have a pair of clusters in two datacenters in a master/master
setup and want to migrate one of them to a new datacenter. I'm trying to
determine if this patch will be required for us and would love if someone would
be willing to double check my thinking.
Currently we have
A -> B, B -> A
1. Setup C, create presplit tables with replication_scope enabled on them.
2. Add peer B -> C (New state A -> B, B -> A, B-> C)
3. Copy table on each table from B -> C
4. Stop applications in A
5. Wait for queues from A -> B to clear
6. Remove peer A -> B (New state B -> A, B-> C
7. Remove peer B -> A (New state B -> C)
8. Add peer C -> B (New state B -> C, C -> B)
9. Start applications in C
Given that we can live with applications only running in a single datacenter
for a period of time we don't ever need to have writes from one cluster
replicate to a downstream loop. Therefore I don't think this patch is required
for this migration. Does that sound correct? So does the state of (A <-> B)
-> C still trigger the problem?
> 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, HBASE-7709-rev1.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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