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From "Ben West (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-3373) Allow regions of specific table to be load-balanced
Date Wed, 30 Nov 2011 17:49:41 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13160177#comment-13160177

Ben West commented on HBASE-3373:

We're running 0.94 and ran into this. With 4 region servers, we had one table with ~1800 regions,
evenly balanced. We then used importtsv to import ~300 regions of a new table. We ended up
with virtually all regions on one server; when I look at the master's log it looks like there
were 159 rebalances (which makes sense); 123 were moving regions from the old table, and 26
moved new table regions. The result is that about 90% of the regions of the new table are
on one server.

When I look at DefaultLoadBalancer.balanceCluster, it has:

        // fetch in alternate order if there is new region server
        if (emptyRegionServerPresent) {
          fetchFromTail = !fetchFromTail;

so we're only doing the randomization stuff in HBASE-3609 if there's a new region server?
Is there a reason we don't do this all the time?
> 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
>         Attachments: HbaseBalancerTest2.java
> 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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