James Taylor created PHOENIX-1146:
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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client is out-of-date.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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