title: How efficient is HDF5 for data retrieval as opposed to data storage?
body: <p>I would like to dump a keyed 500GB table into HDF5, and then then retrieve rows matching specific keys.</p>
  
  <p>For an HDF5 file, items like all the data access uses an integer "row" number, so seems like I would have to implement a 'key to row number map" outside of HDF5. </p>
  
  <p>Isn't retrieval more efficient with a distributed system like Hadoop or Spark which uses HDFS? Should I be using a distributed system to implement the map/hashfunction? </p>