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From "James Taylor (JIRA)" <j...@apache.org>
Subject [jira] [Created] (PHOENIX-1146) Detect stale client region cache on server and retry scans in split regions
Date Tue, 05 Aug 2014 06:38:11 GMT
James Taylor created PHOENIX-1146:
-------------------------------------

             Summary: Detect stale client region cache on server and retry scans in split
regions
                 Key: PHOENIX-1146
                 URL: https://issues.apache.org/jira/browse/PHOENIX-1146
             Project: Phoenix
          Issue Type: Bug
    Affects Versions: 5.0.0, 3.1, 4.1
            Reporter: James Taylor
            Assignee: James Taylor


HBase cannot recover correctly from an aggregate scan run on the coprocessor side (see HBASE-116670).
This can lead to incorrect query results the first time a query is run after a split occurs
(due to the region boundary cache being stale). Phoenix can work around this by:
- detecting on server before the scan starts that the region cache used by the client is out-of-date.
This can be done up-front because the start/stop row of the scan should never span across
a region boundary. In this case, a DoNotRetryIOException is thrown with some embedded information
to cause a StaleRegionBoundaryCacheException to be thrown on the client.
- catching this exception on the client (in ParallelIterators), refreshing the region boundary
cache, and re-running the necessary scans based on the new region boundaries.
- detecting if this happens more than N times to prevent any kind of excessive looping due
to splits occurring over and over again.

Phoenix has additional requirements above and beyond standard HBase clients, so even if HBase
could recover from this situation, Phoenix would likely need this workaround to ensure that
a scan does not span across region boundaries. This is required when the client is doing a
merge sort on the results of the parallel scans, mainly in ORDER BY (including topN) and local
indexing, and potentially GROUP BY if we move toward sorting the distinct groups on the server
side.



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