public synchronized void removeRegionFromTable(RegionInfo hri) throws IOException {
    String namespace = hri.getTable().getNamespaceAsString();
    NamespaceTableAndRegionInfo nsInfo = nsStateCache.get(namespace);
    if (nsInfo != null) {
      nsInfo.decrementRegionCountForTable(hri.getTable(), 1);
    } else {
      throw new IOException("Namespace state found null for namespace : " + namespace);
    }
  }
Initialize namespace state cache by scanning meta table.
hbase-server/src/main/java/org/apache/hadoop/hbase/namespace/NamespaceStateManager.java