Re: Slow count(*) again...

On Oct 12, 2010, at 8:54 AM, <david(at)lang(dot)hm> wrote:

> On Tue, 12 Oct 2010, Craig Ringer wrote:
>
>> On 10/12/2010 04:22 PM, david(at)lang(dot)hm wrote:
>>
>>> from a PR point of view, speeding up the trivil count(*) case could be
>>> worth it, just to avoid people complaining about it not being fast.
>>
>> At the cost of a fair bit more complexity, though, and slowing everything
>> else down.
>
> complexity probably, although given how complex the planner is already is
> this significant?
>
> as far as slowing everything else down, why would it do that? (beyond the
> simple fact that any new thing the planner can do makes the planner take a
> little longer)
>
> David Lang
>
I wouldn't even expect the planner to do more work. An Index Scan can simply avoid going to the tuples for visibility under some circumstances.