I newer talked about persistent data. I talked about persistent metadata.
Sure, I finally understood that detail. Now if I hear "persistent variable", I by default understand that both metadata and data are persistent... It requires some effort to understand the subtelty.
I really don't propose any possible substitution of tables (relations). I newer did it.
Sure.
The used terminology is not 100% clean and natural - maybe better name is "global temporary unshared untransactional unrelational storage" -
Hmmm. Too long:-) But these properties need to be spelled out.
[...] I don't see any sense to have two similar storages or two redundant access methods - not in PostgreSQL level.
Then say so in the wiki in the cons.
Personnaly, I'm not sure. Maybe having a clean way of declaring a one-row "singleton" table enforced by postgresql would be enough.
There is a singleton table :)
create table foo(x integer unique not null default 1 check(x = 1), y integer);
insert into foo(y) values(100);
analyze foo;
The storage is not important and is not interesting - any different behave for persistent objects different than MVCC can be big surprise for users.
our sequences - simple, persistent, and not ACID - I found lot of people that cannot accept it - not quickly
What is interesting are getter functions - they can be volatile or stable/immutable - what can be interesting, because then the value can be used by planner.
For example - MySQL @var is volatile - can be changed in query - that's mean, you cannot use it as const for planner :( - the behave will be same (with same risks to performance) like using plpgsql variable in query.