@Override
      protected void run() throws IOException {
        getMaster().getMasterCoprocessorHost().preMergeRegions(regionsToMerge);
        String aid = getClientIdAuditPrefix();
        LOG.info("{} merge regions {}", aid, regionNamesToLog);
        submitProcedure(new MergeTableRegionsProcedure(procedureExecutor.getEnvironment(),
          regionsToMerge, forcible));
        getMaster().getMasterCoprocessorHost().postMergeRegions(regionsToMerge);
      }
Switch for the background CatalogJanitor thread. Used for testing. The thread will continue to
run. It will just be a noop if disabled.
@param b If false, the catalog janitor won't do anything.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java