Re: CUDA Sorting

On Sep 19, 2011, at 5:16 PM, Tom Lane wrote:

> Greg Stark <stark(at)mit(dot)edu> writes:
>> That said, to help in the case I described you would have to implement
>> the tapesort algorithm on the GPU as well.
>
> I think the real problem would be that we are seldom sorting just the
> key values. If you have to push the tuples through the GPU too, your
> savings are going to go up in smoke pretty quickly …
>

i would argument along a similar line.
to make GPU code fast it has to be pretty much tailored to do exactly one thing - otherwise you have no chance to get anywhere close to card-bandwith.
if you look at "two similar" GPU codes which seem to do the same thing you might easily see that one is 10 times faster than the other - for bloody reason such as memory alignment, memory transaction size or whatever.
this opens a bit of a problem: PostgreSQL sorting is so generic and so flexible that i would be really surprised if somebody could come up with a solution which really comes close to what the GPU can do.
it would definitely be interesting to see a prototype, however.

btw, there is a handful of interesting talks / lectures about GPU programming provided by the university of chicago (just cannot find the link atm).

regards,

hans

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