stack created HBASE-17733:
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Summary: Undo registering regionservers in zk with ephemeral
nodes; its more trouble than its worth
Key: HBASE-17733
URL: https://issues.apache.org/jira/browse/HBASE-17733
Project: HBase
Issue Type: Brainstorming
Reporter: stack
Elsewhere, we are undoing the use of ZK (replication current WAL offset,
regions-in-transition, etc).
I have another case where using ZK, while convenient (call-backs), has holes.
The scenario is prompted by review of HBASE-9593.
Currently, a RS registers with the Master by calling the Master's
reportForDuty. After the Master responds with the name we are to use for
ourselves (as well as other properties we need to 'run'), we then turnaround
and do a new RPC out to the zk ensemble to register an ephemeral znode for the
RS.
We notice a RS has gone away -- crashed -- because its znode evaporates and the
Master has a watcher triggered notifying it the RS has gone (after a zk session
timeout of tens of seconds). Cumbersome (Setting watchers, zk session
timeouts) and indirect. Master then trips the server shutdown handler which
does reassign of regions from the crashed server.
In HBASE-9593, we were trying to handle the rare but possible case where the RS
would die after registering w/ the Master but before we put up our ephemeral
znode. In this case a RS would live in the Master's internals forever because
there is no ephemeral znode to expire to do cleanup and removal of the
never-started RS.
Lets get ZK out of the loop. Then only the Master and RS involved heartbeating
each other.
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