private WAL getWAL(String group) throws IOException {
    WALProvider provider = cached.get(group);
    if (provider == null) {
      Lock lock = createLock.acquireLock(group);
      try {
        provider = cached.get(group);
        if (provider == null) {
          provider = createProvider(group);
          listeners.forEach(provider::addWALActionsListener);
          cached.put(group, provider);
        }
      } finally {
        lock.unlock();
      }
    }
    return provider.getWAL(null);
  }
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