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From "Bryan Duxbury (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-420) Adjacent small regions should be automatically merged
Date Wed, 06 Feb 2008 23:43:08 GMT
Adjacent small regions should be automatically merged
-----------------------------------------------------

                 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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