Re: significant slowdown of HashAggregate between 9.6 and 10

Hi,

On 2020-06-04 18:22:03 -0700, Jeff Davis wrote:
> On Thu, 2020-06-04 at 11:41 -0700, Andres Freund wrote:
> > +/* minimum number of initial hash table buckets */
> > +#define HASHAGG_MIN_BUCKETS 256
> > 
> > 
> > I don't really see much explanation for that part in the commit,
> > perhaps
> > Jeff can chime in?
> 
> I did this in response to a review comment (point #5):
> 
> 
> https://www.postgresql.org/message-id/20200219191636.gvdywx32kwbix6kd@development
> 
> Tomas suggested a min of 1024, and I thought I was being more
> conservative choosing 256. Still too high, I guess?

> I can lower it. What do you think is a reasonable minimum?

I don't really see why there needs to be a minimum bigger than 1?

Greetings,

Andres Freund