Re: 7.4 compatibility question

Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:

> Michael Brusser wrote:
>
> > Optimizer improvements
> > => this tells me nothing. I suppose this could be a minor internal code
> > tweak, which does not affect me. On the other hand this could be a major
> > breakthrough, so now I can run some stupid query which would take
> > a week to complete in the previous release. How do I know?
>
> Yes, this is always very hard to explain. The optimizer itself is
> complex, and uses complex terms like merge join and key pruning. It is
> hard to explain what queries will be affected, though the basic issue is
> that the optimizer will choose a better plan more frequently.

One thing that might be worth mentioning is that "WHERE foo IN (subquery)"
type queries are much improved. That's a one of the more common complaints
about 7.3 and previous and it's one that fairly easy to recognize.

--
greg