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

On Tue, Jun 26, 2012 at 9:50 AM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:
> 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.

But with a small change to psql they could, without the need for a
whole new type of variable. For example, psql could set all those
variable as "psql.<commandlinevarname>", which could then be accessed
from the DO PL code just fine.

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