Region balancer oscillates during cluster startup
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Key: HBASE-615
URL: https://issues.apache.org/jira/browse/HBASE-615
Project: Hadoop HBase
Issue Type: Bug
Components: master
Affects Versions: 0.2.0
Reporter: Jim Kellerman
Assignee: Bryan Duxbury
When starting a cluster with four region servers and a large table (49 regions)
(+root +meta) = 51 total regions, the region balancer oscillates for a very
long time and does not seem to reach a steady state.
Additionally, for whatever reason, it seems reluctant to assign regions to the
first of four region servers, which may be the root cause. In my test, the
first server had 10 regions assigned, the second and fourth had 13 regions
assigned, and the master would continually assign and deassign 2 regions to the
third server, which oscillated between 13 and 15 regions. If it assigned the
two fluctuating regions to the first server, it would achieve the best balance
possible: 12, 13, 13, 13.
After 20 minutes, it had not stopped oscillating. An application trying to work
against this cluster would run very slowly as it would be continually
re-finding the two regions in flux.
When the table was being created, regions were nicely balanced. On restart,
however, it just would not settle down.
Perhaps the balancer should set a target number of regions for each server
which when the server achieved +/- 1 regions, the rebalancer would not try to
change unless the number of regions changed.
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