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.
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.
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.