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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-7709) Infinite loop possible in Master/Master replication
Date Wed, 28 Aug 2013 20:58:53 GMT

     [ https://issues.apache.org/jira/browse/HBASE-7709?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Lars Hofhansl updated HBASE-7709:

    Attachment: 7709-0.94-rev6.txt

Discussed offline with Vasu.
Proposing one small change: Don't store the first cluster in an edit twice. So the clusterID
as used now holds the first cluster id and the new clusterIds in Mutation and Scopes on the
WALEdit hold the 2nd and 3rd cluster ID if any.
As master <-> master replication will be the most common scenario this seems an important
> 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
>            Assignee: Vasu Mariyala
>             Fix For: 0.98.0, 0.94.12, 0.96.0
>         Attachments: 095-trunk.patch, 0.95-trunk-rev1.patch, 0.95-trunk-rev2.patch, 0.95-trunk-rev3.patch,
0.95-trunk-rev4.patch, 7709-0.94-rev6.txt, HBASE-7709.patch, HBASE-7709-rev1.patch, HBASE-7709-rev2.patch,
HBASE-7709-rev3.patch, HBASE-7709-rev4.patch, HBASE-7709-rev5.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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