Re: count(*) performance improvement ideas

Joe Conway <mail(at)joeconway(dot)com> writes:
> Tom Lane wrote:
>> I thought about this in the shower just now, and ISTM that if we want to
>> turn this into an actual feature rather than a kluge, there needs to be
>> some sort of "define variable" command that sets up a custom variable
>> and specifies its type (and whatever other properties seem worth
>> setting). IOW expose the DefineCustomFooVariable functions to SQL users.
>>
>> I'd be a bit inclined to restrict the namespace that can be set up that
>> way, eg allow only "local." or "session." as the prefix. Maybe
>> that's just being too anal, but we could guarantee not to introduce
>> colliding built-in GUCs in future releases, whereas people trying to
>> define variables with any random name would definitely be at risk.

> Would it make sense to have built-in GUCs belong to "pg_catalog." and
> user defined GUCs default to "public."?

[ after a bit of reflection... ] I don't think that we want to tie
GUC names to schemas, especially not schemas that might not be there
(remember public is droppable). The existing scheme for qualified
GUC names considers that the prefix is the name of a loadable module,
which isn't typically tied to any particular schema.

I kinda like "session" as the prefix since it helps remind people that
these things will have session lifespan.

OTOH, there's a possibility for confusion with the SET SESSION syntax
("hm, did you mean SET SESSION foo = ... or SET session.foo = ...?").
"local" has got the same issue. Maybe "temp"?

regards, tom lane