@RestrictedApi(explanation = "Should only be called in tests", link = "",
      allowedOnPath = ".*/src/test/.*")
  public String getFactoryId() {
    return this.factoryId;
  }
Returns all the wal providers, for example, the default one, the one for hbase:meta and the one
for hbase:replication.
hbase-server/src/main/java/org/apache/hadoop/hbase/wal/WALFactory.java