CUDA Sorting

Hello everyone,

I'm implementing a CUDA based sorting on PostgreSQL, and I believe it
can improve the ORDER BY statement performance in 4 to 10 times. I
already have a generic CUDA sort that performs around 10 times faster
than std qsort. I also managed to load CUDA into pgsql.

Since I'm new to pgsql development, I replaced the code of pgsql
qsort_arg to get used with the way postgres does the sort. Everything
looks easy and "GPU-able". The only problem is that I can't use the
qsort_arg_comparator comparator function on GPU, I need to implement
my own. I didn't find out how to access the sorting key value data of
the tuples on the Tuplesortstate or SortTuple structures. If I solve
this problem I'll make a really big step forward.

Cheers,
Vítor Uwe Reus