Re: [PATCH] Negative Transition Aggregate Functions (WIP)

Florian Pflug <fgp(at)phlo(dot)org> writes:
> On Jan10, 2014, at 19:08 , Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Although, having said that ... maybe "build your own aggregate" would
>> be a reasonable suggestion for people who need this? I grant that
>> it's going to be a minority requirement, maybe even a small minority
>> requirement. People who have the chops to get this sort of thing right
>> can probably manage a custom aggregate definition.

> So we'd put a footgun into the hands of people who don't know what they're
> doing, to be fired for performance's sake, and leave it to the people
> who know what they are doing to put the safety on?

If I may put words in Kevin's mouth, I think his point is that having
float8 sum() at all is a foot-gun, and that's hard to deny. You need
to know how to use it safely.

A compromise compromise might be to provide these alternative "safer"
aggregates built-in. Or, depending on what color you like your bikeshed,
leave the standard aggregates alone and define "fast_sum" etc for the less
safe versions. In any case it'd be incumbent on us to document the
tradeoffs.

regards, tom lane