Re: bad JIT decision

Hi,

On Fri, Jul 24, 2020, at 15:32, Scott Ribe wrote:
> > On Jul 24, 2020, at 4:26 PM, David Rowley <dgrowleyml@gmail.com> wrote:
> > 
> > It does not really take into account the cost of jitting.
> 
> That is what I was missing.
> 
> I read about JIT when 12 was pre-release; in re-reading after my post I 
> see that it does not attempt to estimate JIT cost. And in thinking 
> about it, I realize that would be next to impossible to anticipate how 
> expensive LLVM optimizstion was going to be.

We certainly can do better than now.

> In the case where a set of functions is replicated across partitions, 
> it would be possible to do them once, then project the cost of the 
> copies. 

Probably not - JITing functions separately is more expensive than doing them once... The bigger benefit there is to
avoidoptimizing functions that are likely to be the same.
 

> Perhaps for PG 14 as better support for the combination of JIT 
> optimization and highly-partitioned data ;-)

If I posted a few patches to test / address some of these issue, could you test them with your schema & querries?

Regards,

Andres