default Map<K, V> getAll(Collection<K> keys) {
    try {
      return getAllAsync(keys).get();
    } catch (InterruptedException | ExecutionException e) {
      throw new SamzaException("GET_ALL failed for " + keys, e);
    }
  }
Fetch the table {@code records} for specified {@code keys}. This method must be thread-safe.
The default implementation calls getAllAsync and blocks on the completion afterwards.
@param keys keys for the table records
@return all records for the specified keys.
samza-api/src/main/java/org/apache/samza/table/remote/TableReadFunction.java