Re: Schema variables - new implementation for Postgres 15

> On Fri, Nov 04, 2022 at 03:17:18PM +0100, Pavel Stehule wrote:
> > I've stumbled upon something that looks weird to me (inspired by the
> > example from tests):
> >
> > =# create variable v2 as int;
> > =# let v2 = 3;
> > =# create view vv2 as select coalesce(v2, 0) + 1000 as result
> >
> > =# select * from vv2;
> > result
> > --------
> > 1003
> >
> > =# set force_parallel_mode to on;
> > =# select * from vv2;
> > result
> > --------
> > 1000
> >
> > In the second select the actual work is done from a worker backend.
> > Since values of session variables are stored in the backend local
> > memory, it's not being shared with the worker and the value is not found
> > in the hash map. Does this suppose to be like that?
> >
>
> It looks like a bug, but parallel queries should be supported.
>
> The value of the variable is passed as parameter to the worker backend. But
> probably somewhere the original reference was not replaced by parameter
>
> On Fri, Nov 04, 2022 at 10:17:13PM +0800, Julien Rouhaud wrote:
> Hi,
>
> There's code to serialize and restore all used variables for parallel workers
> (see code about PARAM_VARIABLE and queryDesc->num_session_variables /
> queryDesc->plannedstmt->sessionVariables). I haven't reviewed that part yet,
> but it's supposed to be working. Blind guess would be that it's missing
> something in expression walker.

I see, thanks. I'll take a deeper look, my initial assumption was due to
the fact that in the worker case create_sessionvars_hashtables is
getting called for every query.