Re: pgsql: Remove item, not sure what it refers to:

* Bruce Momjian (pgman(at)candle(dot)pha(dot)pa(dot)us) wrote:
> Thanks, TODO item readded with a clearer description:
>
> * Allow ORDER BY ... LIMIT 1 to select high/low value without sort or
> index using a sequential scan for highest/lowest values
>
> Right now, if no index exists, ORDER BY ... LIMIT 1 requires we sort
> all values to return the high/low value. Instead The idea is to do a
> sequential scan to find the high/low value, thus avoiding the sort.

Could we take this perhaps a step further and consider things like
'LIMIT 10' and come up with an approximate point where the trade-off
exists? Actually, thinking about this a minute more perhaps there isn't
even a trade-off to be made... What you're suggesting is basically a
size-of-1 temporary memory structure for the 'sort'. Isn't there
already a memory structure used to perform the sorting though? Could it
be adjusted such that it's of a fixed size when 'LIMIT' is given, as
above?

Just some thoughts, while I think the specific 'LIMIT 1' case is
probably pretty common I think the 'LIMIT 10' or 'LIMIT 50' (or however
many you want to display on the webpage...) is a pretty common use case
too and it sounds like we could improve those too with this mechanism.

Thoughts?

Thanks,

Stephen