Adjacent small regions should be automatically merged
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Key: HBASE-420
URL: https://issues.apache.org/jira/browse/HBASE-420
Project: Hadoop HBase
Issue Type: Improvement
Components: master, regionserver
Reporter: Bryan Duxbury
Priority: Minor
Region merge functionality exists in HBase today, but merges are triggered
manually (in theory only, because there is no admin tool for doing so). Instead
of relying on an admin to note and merge regions, the Master should detect
adjacent undersized regions and automatically merge them.
Other than the case when a table has exactly one region, region sizes should
always be between 1/2x and 1x the split size. For instance, if the max file
size is 256MB, steady-state, regions will be between 128 and 256MB. If we find
two regions near each other that are less than some threshold when summed
together, they are candidates for merging. For instance, we could set the
threshold to 1/2x max file size, so if one region was 50MB and the other was
16MB, they would be mergeable.
The only time that regions small enough to merge should exist is when there
have been significant deletions. Otherwise, regions will always stay in the 1/2
to 1x range.
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