this will be put in the 1_2_0 perf branch, and if results are positive will be forward-ported into trunk.
branch RHQ_1_2_0_GA_PERF: rev4859 - use cached value for agent-is-backfilled;
rev5077 - use cached value for agent-is-backfilled logic;
during dbupgrade, make sure all rhq_agent.backfilled columns have values before setting the column to non-null;
only set agent backfilled if the bit is actually flipping to reduce number of writes in steady state;
move the setting of agent backfilled to false into availabilityManager.updateLastAvailabilityReport, which executes in its own xaction;
rev5078 - always make sure that setting of the agent backfilled bit occurs in a new transaction;
This bug was previously known as http://jira.rhq-project.org/browse/RHQ-2335