[hbase] Keep lazy cache of regions in client rather than an 'authoritative' list
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Key: HADOOP-2443
URL: https://issues.apache.org/jira/browse/HADOOP-2443
Project: Hadoop
Issue Type: Improvement
Components: contrib/hbase
Reporter: stack
Currently, when the client gets a NotServingRegionException -- usually because
its in middle of being split or there has been a regionserver crash and region
is being moved elsewhere -- the client does a complete refresh of its cache of
region locations for a table.
Chatting with Jim about a Paul Saab upload issue from Saturday night, when
tables are big comprised of regions that are splitting fast (because of bulk
upload), its unlikely a client will ever be able to obtain a stable list of all
region locations. Given that any update or scan requires that the list of all
regions be in place before it proceeds, this can get in the way of the client
succeeding when the cluster is under load.
Chatting, we figure that it better the client holds a lazy region cache: on
NSRE, figure out where that region has gone only and update the client-side
cache for that entry only rather than throw out all we know of a table every
time.
Hopefully this will fix the issue PS was experiencing where during intense
upload, he was unable to get/scan/hql the same table.
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