Sketch implementation does not seem to implement a count-min sketch
romaindoumenc opened this issue · comments
In sketch.go, each row is using a custom seed that is xored with the hash value:
val := s.rows[i].get((hashed ^ s.seed[i]) & s.mask)
Note that the two operations are without any sort of bit shifting, meaning that only the masked bits are xored together.
Unless I am mistaken, this mean that all rows in the count-min sketch are effectively the same (shifted), and this in turn means that only one row would give exactly the same information – the tests currently only tests that the rows are not exactly the same, which a fairly low bar.
An effective solution with minimal changes to the current implementation would be to use different masks on each row.
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