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From "Ma, Ming" <min...@ebay.com>
Subject region transition trace
Date Fri, 02 Sep 2011 22:48:03 GMT
Perhaps this feature was discussed before. we currently don't have the full transition history
of all regions { fromState, ToState, the machine that initiates it }; the states will be removed
from zookeeper /hbase/unassigned once the region is assigned; also ".META." table has max
version of 10 thus only tracks the last 10 RS assignments of a given region.

One idea is to put such transition history data to zookeeper. One issue is it could blow up
zookeeper memory if we have large number of regions and the cluster runs for a long time.
I would like to get your feedback on different approaches to address the issue. One assumption
is region assignment doesn't happen with high frequency and thus the overhead introduced won't
have much impact on the system performance.

Approach 1:

Zookeeper knows the history of how /hbase/unassigned is modified, if we can get zookeeper's
logs (Bookkeeper ? ) somehow, we know the history of region transition.

Approach 2:

1.      HBase logs extra region transition data to zookeeper. It could be one zookeeper node
per transaction.
2.      Have a separate thread on the Master to move data from zookeeper and append to HDFS.
That will keep the zookeeper size in check.
3.      Have some tool or web UI to show the history of a given region by looking at zookeeper
and HDFS.


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