confmaster/src/main/java/com/navercorp/nbasearc/confmaster/server/workflow/MembershipGrantWorkflow.java
private void cleanMGen() throws MgmtZooKeeperException {
        try {
        	PartitionGroup.PartitionGroupData pgM = pg.clonePersistentData();
            pgM.cleanMGen(config.getClusterPgMgenHistorySize());
            zk.setData(pg.getPath(), pgM.toBytes(), -1);
            pg.setPersistentData(pgM);
        } catch (Exception e) {
            throw new MgmtZooKeeperException(
                    "Clean mgen history of " + pg + " fail, "
                            + e.getMessage());
        }
    }
private void cleanMGen() throws MgmtZooKeeperException {
        try {
        	PartitionGroup.PartitionGroupData pgM = pg.clonePersistentData();
            pgM.cleanMGen(config.getClusterPgMgenHistorySize());
            zk.setData(pg.getPath(), pgM.toBytes(), -1);
            pg.setPersistentData(pgM);
        } catch (Exception e) {
            throw new MgmtZooKeeperException(
                    "Clean mgen history of " + pg + " fail, "
                            + e.getMessage());
        }
    }
/*
When all PGSes in a PG are green, it is able to
clean mgen-history of PG to prevent history from growing
too long to cause slow operations.