Hi,
I just started evaluating MADlib and one of the first things I tried is how
it performs for dot product and cosine similarity.
So first I set up some test data (1000000 rows of 150element float8[])
Then I ran array_dot and cosine_similarity on it:
select * from (
select cosine_similarity  or array_dot
(a_vector, (select array_agg(random()::float8) from generate_series(0,
150))) c
from vectors
) x
order by c desc
limit 10
On my machine, cosine_similarity takes 1.3s while array_dot takes 3s, which
is rather unexpected... I would have expected a dot product to be much
faster than calculating cosine similarity.
Can anyone shed some light on this?
Thanks,
Mauricio
