Devaraj Das created HBASE-9095:
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Summary: AssignmentManager's handleRegion should respect the
single threaded nature of the processing
Key: HBASE-9095
URL: https://issues.apache.org/jira/browse/HBASE-9095
Project: HBase
Issue Type: Bug
Reporter: Devaraj Das
While debugging a case where a region was getting opened on a RegionServer and
then closed soon after (and then never re-opened anywhere thereafter), it
seemed like the processing in handleRegion to do with deletion of ZK nodes
should be non-asynchronous. This achieves two things:
1. The synchronous deletion prevents more than one processing on the same event
data twice. Assuming that we do get more than one notification (on let's say,
region OPENED event), the subsequent processing(s) in handleRegion for the same
znode would end up with a zookeeper node not found exception. The return value
of the data read would be null and that's already handled. If it is
asynchronous, it leads to issues like - master opens a region on a certain
RegionServer and soon after it sends that RegionServer a close for the same
region, and then the znode is deleted.
2. The deletion is currently handled in an executor service. This is
problematic since by design the events for a given region should be processed
in order. By delegating a part of the processing to executor service we are
somewhat violating this contract since there is no guarantee of the ordering in
the executor service executions...
Thanks to [~jeffreyz] and [~enis] for the discussions on this issue.
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