Details
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Bug
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Status: Closed
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Major
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Resolution: Incomplete
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0.94.5, 0.95.0, 0.96.0
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None
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None
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Description
We were trying to replicate hbase data over to a new datacenter recently. After we turned on replication and then did our copy tables. We noticed that verify replication had discrepancies.
We ran a list_peers and it returned back both peers, the original datacenter we were replicating to and the new datacenter (this was correct).
When grepping through the logs for a few regionservers we noticed that a few regionservers had the following entry in their logs:
2013-09-26 10:55:46,907 ERROR org.apache.hadoop.hbase.replication.regionserver.ReplicationSourceManager: Error while adding a new peer java.net.UnknownHostException: xxx.xxx.flurry.com (this was due to a transient dns issue)
Thus a very small subet of our regionservers were not replicating to this new cluster while most were.
We probably don't want to abort if this type of issue comes up, it could potentially be fatal if someone does an "add_peer" operation with a typo. This could potentially shut down the cluster.
One solution I can think of is keeping some flag in ReplicationSourceManager which is a boolean that keeps track of whether there was an errorAddingPeer. Then in the logPositionAndCleanOldLogs we can do something like:
if (errorAddingPeer) { LOG.error("There was an error adding a peer, logs will not be marked for deletion"); return; }
thus we are not deleting these logs from the queue. You will notice your replicating queue rising on certain machines and you can still replay the logs, thus avoiding a lengthy copy table.
I have a patch (with unit test) for the above proposal, if everyone thinks that is an okay solution.
An additional idea would be to add some retry logic inside the PeersWatcher class for the nodeChildrenChanged method. Thus if there happens to be some issue we could sort it out without having to bounce that particular regionserver.
Would love to hear everyones thoughts.