private void loadRegionsFromInMemoryState(final HbckReport report) {
    List<RegionState> regionStates =
      master.getAssignmentManager().getRegionStates().getRegionStates();
    for (RegionState regionState : regionStates) {
      RegionInfo regionInfo = regionState.getRegion();
      if (
        master.getTableStateManager().isTableState(regionInfo.getTable(), TableState.State.DISABLED)
      ) {
        report.getDisabledTableRegions().add(regionInfo.getRegionNameAsString());
      }
      // Check both state and regioninfo for split status, see HBASE-26383
      if (regionState.isSplit() || regionInfo.isSplit()) {
        report.getSplitParentRegions().add(regionInfo.getRegionNameAsString());
      }
      HbckRegionInfo.MetaEntry metaEntry = new HbckRegionInfo.MetaEntry(regionInfo,
        regionState.getServerName(), regionState.getStamp());
      report.getRegionInfoMap().put(regionInfo.getEncodedName(), new HbckRegionInfo(metaEntry));
    }
    LOG.info("Loaded {} regions ({} disabled, {} split parents) from in-memory state",
      regionStates.size(), report.getDisabledTableRegions().size(),
      report.getSplitParentRegions().size());
    if (LOG.isDebugEnabled()) {
      Map<RegionState.State, Integer> stateCountMap = new HashMap<>();
      for (RegionState regionState : regionStates) {
        stateCountMap.compute(regionState.getState(), (k, v) -> (v == null) ? 1 : v + 1);
      }
      StringBuffer sb = new StringBuffer();
      sb.append("Regions by state: ");
      stateCountMap.entrySet().forEach(e -> {
        sb.append(e.getKey());
        sb.append('=');
        sb.append(e.getValue());
        sb.append(' ');
      });
      LOG.debug(sb.toString());
    }
    if (LOG.isTraceEnabled()) {
      for (RegionState regionState : regionStates) {
        LOG.trace("{}: {}, serverName={}", regionState.getRegion(), regionState.getState(),
          regionState.getServerName());
      }
    }
  }
Scan hbase:meta to get set of merged parent regions, this is a very heavy scan.
@return Return generated {@link HashSet}
hbase-server/src/main/java/org/apache/hadoop/hbase/master/hbck/HbckChore.java