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From "Jonathan Gray (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-3373) Allow regions of specific table to be load-balanced
Date Sat, 18 Dec 2010 21:22:01 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12972870#action_12972870

Jonathan Gray commented on HBASE-3373:

On cluster startup in 0.90, regions are assigned in one of two ways.  By default, it will
attempt to retain the previous assignment of the cluster.  The other option which I've also
used is round-robin.  This will evenly distribute each table.

That plus the change to do round-robin on table create should probably cover per-table distribution
fairly well.

I think the next step in the load balancer is a major effort to switch to something with more
of a cost-based approach.  I think ideally you don't need even distribution of each table,
you want even distribution of load.  If one hot table, it will get evenly balanced anyways.

One thing we could do is get rid of all random assignments and always try to do some kind
of quick load balance or round-robin.  It does seem like randomness always leads to one guy
who gets an unfair share :)

> Allow regions of specific table to be load-balanced
> ---------------------------------------------------
>                 Key: HBASE-3373
>                 URL: https://issues.apache.org/jira/browse/HBASE-3373
>             Project: HBase
>          Issue Type: Improvement
>          Components: master
>    Affects Versions: 0.20.6
>            Reporter: Ted Yu
>             Fix For: 0.90.1
> From our experience, cluster can be well balanced and yet, one table's regions may be
badly concentrated on few region servers.
> For example, one table has 839 regions (380 regions at time of table creation) out of
which 202 are on one server.
> It would be desirable for load balancer to distribute regions for specified tables evenly
across the cluster. Each of such tables has number of regions many times the cluster size.

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