Friday, October 18, 2013

How to generate murmur3 in cassandra2.0

Reading into this doc, got really curious on how the murmur3 hash value is generated.

So I dig at cassandra github, found this this class , it seem that, cassandra 2.0 generate the token for the primary key using this method hash3_x64_128. Below are the method to get it work.. just put this into any java class and see the token generated.


public static LongToken genToken(String rowKey) {
ByteBuffer key = ByteBufferUtil.bytes(rowKey);
long hash = MurmurHash.hash3_x64_128(key, key.position(), key.remaining(), 0)[0];
LongToken lk = new LongToken(normalize(hash));
return lk;

public static void main(String[] args) {

private static long normalize(long v)
// We exclude the MINIMUM value; see getToken()
return v == Long.MIN_VALUE ? Long.MAX_VALUE : v;


with jim, it generated as 2680261686609811218. So that should be correct. Something extra, if you use nodetool to show the token ranges, e.g. nodetool -h localhost describering jw_schema1, you should get an idea with the token generated, the range on which nodes are responsible that hold the row data.

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