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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-9158) Serious bug in cyclic replication
Date Thu, 08 Aug 2013 06:59:50 GMT
Lars Hofhansl created HBASE-9158:

             Summary: Serious bug in cyclic replication
                 Key: HBASE-9158
                 URL: https://issues.apache.org/jira/browse/HBASE-9158
             Project: HBase
          Issue Type: Bug
    Affects Versions: 0.94.10, 0.95.1, 0.98.0
            Reporter: Lars Hofhansl
            Priority: Critical

While studying the code for HBASE-7709, I found a serious bug in the current cyclic replication
code. The problem is here in HRegion.doMiniBatchMutation:
      Mutation first = batchOp.operations[firstIndex].getFirst();
      txid = this.log.appendNoSync(regionInfo, this.htableDescriptor.getName(),
               walEdit, first.getClusterId(), now, this.htableDescriptor);
Now note that edits replicated from remote cluster and local edits might interleave in the
WAL, we might also receive edit from multiple remote clusters. Hence that <walEdit>
might have edits from many clusters in it, but all are just labeled with the clusterId of
the first Mutation.

Fixing this in doMiniBatchMutation seems tricky to do efficiently (imagine we get a batch
with cluster1, cluster2, cluster1, cluster2, ..., in that case each edit would have to be
its own batch). The coprocessor handling would also be difficult.

The other option is create batches of Puts grouped by the cluster id in ReplicationSink.replicateEntries(...),
this is not as general, but equally correct. This is the approach I would favor.

Lastly this is very hard to verify in a unittest.

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