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.
Ming
