Re: Overhauling GUCS

On Mon, 2008-06-02 at 11:59 -0400, Jignesh K. Shah wrote:
>
> Simon Riggs wrote:
> >
> > Some other problems I see with GUCs
> >
> > * It's not possible to set one parameter depending upon the setting of
> > another.
> >
>
> To me this is more critical.. Most people I have seen will increase one
> or few but not all parameters related to memory which can result in loss
> of performance and productivity in figuring out.
>
> What happened to AvailRAM setting and base all memory gucs on that.
> Ideally PostgreSQL should only create one big memory pool and allow all
> other variables to change runtime via dba or some tuner process or
> customized application as long as total is less than the allocated
> shared_memory and local_memory settings. (This will also reduce the need
> of restarting Postgres if a value needs to be changed)

Agreed.

Right now, we can't even do that in code, let alone in config file.

If we had a smart_memory_config = on then we'd be able to say in the
backend:
if (smart_memory_config)
{
other_thing = 0.1 * Nbuffers;
}

but the GUCs are evaluated in alphabetical order, without any way of
putting dependencies between them. So they are notionally orthogonal.

--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support