Adding xxhash Vindex

[harshit-gangal]

Signed-off-by: Harshit Gangal [email protected]

Added XXHash 64 Bits Vindex to be used for any sql type that are primarily used as Primary Vindex i.e Numbers / Characters.

XXHash is a high quality hashing algorithm having high performance with high Avalanche effect.

Local Benchmarks:

input size	runs	cpu time	data processing speed
8B	169129670	5.96 ns/op	1343.35 MB/s
64B	66039966	17.0 ns/op	3772.40 MB/s
512B	22085480	54.7 ns/op	9365.76 MB/s
1KB	12024784	95.8 ns/op	10433.92 MB/s
4KB	2842335	355 ns/op	11272.72 MB/s

[sougou]

Looks like this is a better alternative than binary_md5. Some people may eventually want a unicode_loose_xxhash eventually.

[harshit-gangal]

I believe it can be extended to support multi-column Vindex. As the xxHash works on bytes it is sql column type agnostic and also allow multiple bytes to be added to generate a single 64 bit hash.