Loading data from memory tends to be the most expensive part of the comparison
operations. Because we don't have a tri_compare function for tokens, we end up
having to do an equality test, which will load the token's data in memory, and
then, because all we know is that they are not equal, we need to do another
one.
Having two dereferences is harmful, and shows up in my simple benchmark. This
is because before writing to sstables, we must order the keys in decorated key
order, which is heavy on the comparisons.
The proposed change speeds up index write benchmark by 8.6%:
Before:
41458.14 +- 1.49 partitions / sec (30 runs)
After:
45020.81 +- 3.60 partitions / sec (30 runs)
Parameters:
--smp 6 --partitions 500000
Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
e1968c389e