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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HBASE-1019) Master should reassign regions away from regionservers under heap stress
Date Mon, 01 Dec 2008 08:32:44 GMT

     [ https://issues.apache.org/jira/browse/HBASE-1019?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Andrew Purtell updated HBASE-1019:

    Attachment: 1019.patch

There are two parts of the attached patch, that don't necessarily have to go in together.

1) Regionservers will relinquish meta regions by closing them proactively if under heap stress.
Heap stress is defined as available heap falling below a minimum threshold (20MB) even after
forced GC. Hysteresis is applied via a two minute waiting time between assignment of a region
and a close of it, so even if all regionservers are under heap stress a meta region will find
a home. 

2) Some changes to HServerLoad make load comparisons heap aware. 
- If the number of regions is less, but heap use is greater, consider the load higher. Otherwise,
- If the number of regions is greater, the load is always greater.
- If the number of regions is equal, the load difference is determined by heap usage.

I'm not advocating this patch go in right away. There are some questions:

Item #1 above will close ROOT. Will the master be able to recover from this? (It will also
close META regions, but I think this is ok.)

Item #2 above will change the behavior of the balancer and should be tested on a cluster first.

> Master should reassign regions away from regionservers under heap stress
> ------------------------------------------------------------------------
>                 Key: HBASE-1019
>                 URL: https://issues.apache.org/jira/browse/HBASE-1019
>             Project: Hadoop HBase
>          Issue Type: Improvement
>          Components: master, regionserver
>            Reporter: Andrew Purtell
>             Fix For: 0.19.0
>         Attachments: 1019.patch
> Once the changes for HBASE-1018 go in, the master should reassign regions away from regionservers
that indicate heap stress to those that do not. Reassignment activity must be smart enough
not to overload remaining regionservers.

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