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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