[ACCUMULO-751] Support Wire Compatibility (between bugfix releases)

• Type: Improvement
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 1.4.0
• Fix Version/s: 1.5.0
• Component/s: master, rpc, tserver
• Labels: api compatibility versioning wire wireprotocol
• Assignee: Christopher Tubbs
• Reporter: Mike Drob
• Created: 05/Sep/12 00:49
• Updated: 07/Jun/13 21:44
• Resolved: 25/Jan/13 21:58

Description

With the advent of the HA NameNode in HDFS, the need for planned Hadoop outages has greatly diminished. I believe that Accumulo should follow suit and eventually allow for no-outage upgrades.

To support this feature, we would require wire compatibility between different versions so that the cluster can continue to function in a mixed state. There are already contingencies for master fail-over and tservers to leave/join the cluster, so I think this is a natural extension of that code.

To accomplish this for bugfix releases should be trivial. I think it is only necessary to remove (or relax) the version check that happens when a tserver attempts to join. There are rarely (never?) changes to the thrift protocol between bugfix releases, so theoretically a 1.4.1 tserver is already compatible with a 1.4.0 master and vice versa.

To maintain compatibility in the face of thrift protocol changes is certainly a harder challenge, which might be best reserved for a separate ticket.

Issue Links

• is duplicated by: ACCUMULO-662 Accumulo instance with different versions not starting up