| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Peter Geoghegan <pg(at)bowt(dot)ie> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Taylor Vesely <tvesely(at)pivotal(dot)io>, Adam Lee <ali(at)pivotal(dot)io>, Melanie Plageman <mplageman(at)pivotal(dot)io>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Memory-Bounded Hash Aggregation |
| Date: | 2020-02-06 01:54:48 |
| Message-ID: | e6471fd8eedefb8ec1551be955bf30792217e872.camel@j-davis.com |
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| Lists: | pgsql-hackers |
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
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