@Override
  protected long getNumLogFiles0() {
    long numLogFiles = 0;
    for (WALProvider provider : cached.values()) {
      numLogFiles += provider.getNumLogFiles();
    }
    return numLogFiles;
  }
A group-provider mapping, make sure one-one rather than many-one mapping
hbase-server/src/main/java/org/apache/hadoop/hbase/wal/RegionGroupingProvider.java