[GitHub] spark pull request: [SPARK 5280] RDF Loader added + documentation

[set0gut1 <gi...@git.apache.org>]

Github user set0gut1 commented on the pull request:

    https://github.com/apache/spark/pull/4650#issuecomment-154509562
  
    ```scala
    def gethash(in:String):Long = {
      var h = 1125899906842597L
      for (x <- in) {
        h = 31 * h + x;
      }
      return h
    }
    ```
    
    This hash function seems to be weak.
    I tried this with subject URIs of DBpedia's `labels_en.nt` ([sample](http://downloads.dbpedia.org/preview.php?file=2015-04_sl_core-i18n_sl_en_sl_labels_en.nt.bz2)).
    There are 11,519,154 unique URIs, and the hash values of 20,741 URIs collided (0.18%).
    
    For example, the hash values of these URI are same (-3127496886112549146).
    
    * `http://dbpedia.org/resource/Dms`
    * `http://dbpedia.org/resource/EOT`
    * `http://dbpedia.org/resource/F15`
    * `http://dbpedia.org/resource/EP5`


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