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https://issues.apache.org/jira/browse/HBASE-420?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13041708#comment-13041708
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Jean-Daniel Cryans commented on HBASE-420:
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1621 is a lesser version of 420, this jira is about the "perfect" solution
while the former is about just disabling the table without taking down the
whole cluster.
> Adjacent small regions should be automatically merged
> -----------------------------------------------------
>
> Key: HBASE-420
> URL: https://issues.apache.org/jira/browse/HBASE-420
> Project: 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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