Map<String, DataSource> getDataSources() {
    return transactionExecutors.entrySet()
        .stream()
        .collect(Collectors.toMap(Map.Entry::getKey, e -> e.getValue().getDataSource()));
  }
Exposed for integration test usage.
@return a map from datacenter name to {@link DataSource}.
ambry-named-mysql/src/main/java/com/github/ambry/named/MySqlNamedBlobDb.java