Re: proof concept - access to session variables on client side

2012/6/26 Magnus Hagander <magnus(at)hagander(dot)net>:
> On Tue, Jun 26, 2012 at 7:06 AM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:
>> Hello
>>
>> I worked on simple patch, that enable access from server side to
>> client side data. It add two new hooks to libpq - one for returning of
>> local context, second for setting of local context.
>>
>> A motivation is integration of possibilities of psql console together
>> with stronger language - plpgsql. Second target is enabling
>> possibility to save a result of some server side process in psql. It
>> improve vars feature in psql.
>>
>> pavel ~/src/postgresql/src $ cat test.sql
>> \echo value of external paremeter is :"myvar"
>>
>> do $$
>> begin
>>  -- we can take any session variable on client side
>>  -- it is safe against to SQL injection
>>  raise notice 'external parameter accessed from plpgsql is "%"',
>> hgetvar('myvar');
>>
>>  -- we can change this session variable and finish transaction
>>  perform hsetvar('myvar', 'Hello, World');
>> end;
>> $$ language plpgsql;
>>
>> \echo new value of session variable is :"myvar"
>>
>> cat test.sql | psql postgres -v myvar=Hello
>> value of external paremeter is "Hello"
>> NOTICE:  external parameter accessed from plpgsql is "Hello"
>> DO
>> new value of session variable is "Hello, World"
>>
>> This is just proof concept - there should be better integration with
>> pl languages, using cache for read on server side, ...
>>
>> Notices?
>
> Why not just use a custom GUC variable instead? E.g. you could have
> psql SET "psql.myvar='Hello, World'", and then you'd need no changes
> at all in the backend? Maybe have a "shorthand interface" for
> accessing GUCs in psql would help in making it easier, but do we
> really need a whole new variable concept?

GUC variables doesn't help with access to psql's command line
parameters from DO PL code.

Regards

Pavel

>
> --
>  Magnus Hagander
>  Me: http://www.hagander.net/
>  Work: http://www.redpill-linpro.com/