Re: proposal: session server side variables

On 14 October 2016 at 23:09, Pavel Stehule  wrote:

>> but only within the session, right? You're not proposing some kind of
>> inter-backend IPC where one backend sets a session var and another
>> backend accesses it and sees the value set by the first session?
>
> In this moment I propose only local (not shared variables). I hope so access
> can be safe with IMMUTABLE access function.

OK, good. Though I suspect you'll have a hard time with IMMUTABLE
functions and need STABLE.

I don't think it's correct to claim that these vars are immutable,
since that'd allow users to do silly things like build them into index
expressions. Splat.

> Default access function should VOLATILE PARALLEL UNSAFE - but immutable sets
> can be defined and used (and I see a sense of these function, because with
> these function the variables are accessed in query planning time).

I don't really understand the purpose of an immutable variable. It
seems inherently contradictory.

-- Craig Ringer                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services