Re: Cached Query Plans (was: global prepared statements)

>     The hairiness is in the plan dependence (or independence) on parameter  
> values, ideally we only want to cache plans that would be good for all  
> parameter values, only the user knows that precisely. Although it could be  
> possible to examine the column histograms...

If cached plans would be implemented, the dependence on parameter values
could be solved too: use special "fork" nodes in the plan which execute
different sub-plans depending on special parameter values/ranges,
possibly looking up the stats at runtime, so that the plan is in a
compiled state with the "decision points" wired in.

This of course would mean a lot heavier planning and possibly a lot
bigger plans, but you could afford that if you cache the plan. You could
even have a special command to plan a query this way.

Cheers,
Csaba.