Re: Memory-Bounded Hash Aggregation

On Wed, 2020-02-05 at 11:56 -0800, Jeff Davis wrote:
> Regarding the API, I'd like to change it, but I'm running into some
> performance challenges when adding a layer of indirection. If I apply
> the very simple attached patch, which simply makes a separate
> allocation for the tapes array, it seems to slow down sort by ~5%.

I tried a few different approaches to allow a flexible number of tapes
without regressing normal Sort performance. I found some odd hacks, but
I can't explain why they perform better than the more obvious approach.

The LogicalTapeSetExtend() API is a natural evolution of what's already
there, so I think I'll stick with that to keep the scope of Hash
Aggregation under control.

If we improve the API later I'm happy to adapt the HashAgg work to use
it -- anything to take more code out of nodeAgg.c!

Regards,
    Jeff Davis