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From "Ming Ma (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-4354) track region history
Date Thu, 08 Sep 2011 18:34:10 GMT
track region history
--------------------

                 Key: HBASE-4354
                 URL: https://issues.apache.org/jira/browse/HBASE-4354
             Project: HBase
          Issue Type: New Feature
          Components: master, metrics, regionserver
            Reporter: Ming Ma
            Assignee: Ming Ma


For debugging and analysis purposes it will be useful to understand regions' lifecycle, how
it is created ( from which parent region, for example), how it is splitted, assigned, etc.
Some of these info are in the logs, hbase .META. table, zookeeper, metrics. Certain history
data is lost; for example, 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. It will be nice to put it a central place. It can provide:

1. How applications use hbase. For example, it might create large number of regions in a short
period of time and drop the table later.
2. How HBase internally manage regions such as how regions are splitted, assigned, turned
offline, etc.

Things to track
1. How it is created, parent region in the case of split.
2. Region tranisition process such as region state change, region server change.


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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