Re: Tablespace and cpu costs

Gavin Sherry wrote:

> On Wed, 18 Aug 2004, Gaetano Mendola wrote:
>
>
>>Gavin Sherry wrote:
>>
>>
>>>On Wed, 18 Aug 2004, Gaetano Mendola wrote:
>>>
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>>>>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.

That is the goal.

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

I think we need both, I think could be also usefull add a STORE option:

ALTER TABLESPACE RANDOMPAGECOST 0.001 STORE

if the STORE is present then the pg_tablespace.conf is updated

this could be argued with the fact that we do not have SET cpu_costs STORE bu this
doesn't mean that we can not have it in the future :-)

I think is also usefull insert it in the dump "as comment" before the tablespace
creation, this in order to don't loose these setting.

Regards
Gaetano Mendola