Re: Strange count(*) implementation?

Hi Alvaro,

I used to do some research in extensibility of query optimizers to match
the extensibility of the operators. However, it's not really in the
focus of my research anymore so I can't spend much time on it,
unfortunately. I'll keep it in mind in case a student of the group where
I'm working is looking for an project.

Regards,

Henk Ernst.

Alvaro Herrera wrote:

>On Tue, Oct 26, 2004 at 01:56:41PM +0200, Henk Ernst Blok wrote:
>
>Hi,
>
>
>
>>I assume(d) the more expensive statistics (e.g., value distribution
>>info) are updated only when outdated too much or on request (manual
>>vacuum). Usually, other/cheap statistics can easily be maintained
>>incrementally and thus reflect actual table state after each update. Of
>>course, the MVCC principle seems to make things a bit more complicated I
>>understand now.
>>
>>
>
>It's not only MVCC; it's also the fact that aggregates are extensible.
>So to the system they are just opaque functions and it doesn't know how
>to optimize them.
>
>Of course this can be done, e.g. by supplying an optimizing function with
>each aggregate that would try to convert the step-by-step aggregate
>execution plan into a completely different operation (say by looking at
>an index to obtain a max() value), but as you see this is not a trivial
>task, and more importantly, it hasn't been done. Which is to mean, if
>you want to try and submit a patch, it could be improved in the future.
>
>
>

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