Re: Tablespace and cpu costs

On Wed, 18 Aug 2004, Gaetano Mendola wrote:

> Gavin Sherry wrote:
>
> > On Wed, 18 Aug 2004, Gaetano Mendola wrote:
> >>-----BEGIN PGP SIGNED MESSAGE-----
> >>Hash: SHA1
> >>
> >>Hi all,
> >>now that we have the tablespace support don't you think that
> >>each tablespace needs his own costs instead of a system wide
> >>one ?
> >>
> >>I searched in the archives and on the TODO list without success.
> >
> >
> > Yep. I've looked at this but didn't think it necessary for the first stage
> > of implementation.
> >
> > I definately plan to do it for 8.1
>
> Do you have an Idea on how you want implement this ( usage side ) ?
>

Well, as far as I can tell there are two ways we could do it without
reinventing the wheel -- but both are ugly.

The first is to add a parameter to CREATE TABLESPACE and ALTER TABLESPACE
called RANDOMPAGECOST (or something like that) which allows users to set
the random page cost for a given tablespace. I'm undecided as to whether
they should be able to set the sequential scan cost. That seems
reasonable too at first look.

The second option is to have a pg_tablespace.conf file which defines
tablespace specific settings in some way or another.

Either way, the data will be feed into the planner so that the costing
routines will be able to use them.

Anyone else got some thoughts on how we could do this in a cleaner manner?

Gavin