Support for fault tolerant, instant schema updates with out master's intervention
Review Request #1786 - Created Sept. 11, 2011 and updated
From Subbu: here is the latest patch that support alter_instant, an instant schema change command that supports (Add, Modify, Delete column and Modify table) actions through ZK. 1. This pattern capitalizes on the fact that HRI's are now in HDFS and need not be sent over again from Master to RS cloud on every schema change event. 2. Offers real time instant schema change as we bypass the explicit bulk reassign (unassign + assign) of regions from master to RS. 3. Offers fault tolerant schema change support as schema changes now go through ZK. Secondary master taking over a failed schema change will be addressed through a separate JIRA.
Unit tests pass.