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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