public void fix() throws IOException {
    CatalogJanitorReport report = this.masterServices.getCatalogJanitor().getLastReport();
    if (report == null) {
      LOG.info("CatalogJanitor has not generated a report yet; run 'catalogjanitor_run' in "
        + "shell or wait until CatalogJanitor chore runs.");
      return;
    }
    fixHoles(report);
    fixOverlaps(report);
    // Run the ReplicationBarrierCleaner here; it may clear out rep_barrier rows which
    // can help cleaning up damaged hbase:meta.
    this.masterServices.runReplicationBarrierCleaner();
  }
Maximum for many regions to merge at a time.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/janitor/MetaFixer.java