Re: Memory-Bounded Hash Aggregation

On Tue, 2020-02-04 at 18:10 +0200, Heikki Linnakangas wrote:
> I'd love to change the LogicalTape API so that you could allocate
> and 
> free tapes more freely. I wrote a patch to do that, as part of
> replacing 
> tuplesort.c's polyphase algorithm with a simpler one (see [1]), but
> I 
> never got around to committing it. Maybe the time is ripe to do that
> now?

It's interesting that you wrote a patch to pause the tapes a while ago.
Did it just fall through the cracks or was there a problem with it?

Is pause/resume functionality required, or is it good enough that
rewinding a tape frees the buffer, to be lazily allocated later?

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%.

Regards,
    Jeff Davis