Re: extract psql meta-commands into library?

Hello

2014-03-07 16:42 GMT+01:00 Catherine Devlin <catherine(dot)devlin(at)gmail(dot)com>:

> On Thu, Mar 6, 2014 at 12:09 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Hm ... the code in psql's describe.c is not terribly conducive to that.
> > Parsing of the backslash command, execution of the query/queries, and
> > presentation of the results is all rather tightly bound up; you'd have
> > to think about how to decouple those.
>
> I just looked into describe.c, but it was virtually my first look at C
> in 15 years and I'm pretty intimidated.
>
> Come to think of it, I really like the idea of moving the query
> execution and presentation of results out into plpgsql functions in
> template0; then it would be super-easy for applications to utilize
> them. Parsing the command could stay with psql, because the
> applications would probably want to do that parsing themselves,
> anyway.
>

I don't think so using plpgsql can be good idea:

a) client side is better for implementation version independent code

b) possible bugs in plpgsql code should not be fixed without living
database - so any bug release can be significantly more dangerous than now.

Regards

Pavel

>
> The trouble is that psql is written to work against older databases,
> so if the code were stripped from describe.c in favor of calling
> stored functions, those commands would stop working against older
> PostgreSQL installations; and if the code were left in describe.c,
> then the same function would exist in two different forms in two
> different places, with all the maintanability problems that implies.
>
> Is there a way around this I'm not thinking of?
>
> Alternately, I may just give up and write my own, freestanding,
> approximate implementation of the meta-commands with no effort to
> actually replace the native one. It could still be useful to
> application developers if they find out about it.
>
> --
> - Catherine
> http://catherinedevlin.blogspot.com
>
>
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