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https://issues.apache.org/jira/browse/HBASE-7709?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13569623#comment-13569623
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Ted Yu commented on HBASE-7709:
-------------------------------
Looking at HLogKey#readFields():
{code}
if (version.atLeast(Version.INITIAL)) {
if (in.readBoolean()) {
{code}
>From the javadoc of readBoolean():
Reads one input byte and returns true if that byte is nonzero, false if that
byte is zero.
I think there is room to implement option #3 in the description. We can
introduce new version (two, considering compression) where write, instead of
true, the number of hops that HLog.Entry has gone through - starting with 1. A
byte should suffice for this purpose.
+1 on documenting this intricacy for 0.94.x in the refguide.
I think we should create several subtasks for this JIRA.
> 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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