Affects Version/s: None
Fix Version/s: 0.90.0
This is a good one. It happened to me testing OOME in split logging.
- Balancer moves region to new location, regionservrer X.
- New location regionserver X successfully opens the region and then goes to update .META.
- At this point, the server carrying .META. crashes.
- Regionserver X is stuck waiting on .META. to come back online. It takes so long master times out the region-in-transition
- Master assigns the region elsewhere to regionserver Y
- It opens successfully on regionserver Y and then it also parks waiting on .META. coming online
- .META. comes online
- The two servers X and Y race to update .META.
I saw case where server X edit went in after server Ys edit which means that lookups in .META. get the wrong server. HBCK can detect this situation.
RegionServer X when it wakes up coreeclty notices that its lost control of the region but the damage is done – where damage is .META. edit.
Chatting with Jon, he suggested that regionserver X should 'rollback' the .META. edit – do explicit delete of what it added. This would work I think but chatting more, I'll make a fix that keeps updating the zookeeper OPENING state while edit goes on in a separate thread. Our continuous setting of OPENING will make it so region-in-transition does not timeout.