2010/9/9 Darren Duncan <darren@darrenduncan.net>:
> Kevin Grittner wrote:
>>
>> Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>>
>>> to my mind the main thing that would justify inventing a separate
>>> PROCEDURE facility is if procedures were to execute outside the
>>> transaction system, so that they could start and stop transactions
>>> for themselves.
>>
>> That is the biggest distinction in my mind, too. Supporting
>> multiple result sets just as if the queries were run as independent
>> client-side statements would also be very important. I have seen
>> implementations which support, for a single stored procedure, OUT
>> parameters, a RETURN value, and multiple result sets -- all at the
>> same time, as separate things. I haven't reviewed stored procedures
>> in the SQL standard since an early draft proposal years ago, so I
>> don't know what the current state of that is, but if PostgreSQL
>> approaches this, it'd be nice to implement as many of the above as
>> are not in conflict with requirements of the standard.
>
> If it was reasonable I would go further in splitting and have at least 4
> distinct kinds of routines, here listed in order of invocablility (each
> routine kind can invoke anything above it on the list but not anything below
> it):
>
> 1. Expression-invoked pure functions that only have IN parameters and can
> not directly see the database or have any side-effects and are always in a
> transaction. Most operators are of this kind.
>
> 2. Statement-invoked routines that are pure like #1 but also have OUT/INOUT
> parameters instead of resulting in a value like a function. The assignment
> operator is of this kind.
>
> 3. Routines that *can* see and update the database but are otherwise like
> #2, and are always in a transaction. The general case of a SELECT or DML or
> DDL are of this kind.
>
> 4. Routines that can cross transaction boundaries or control transactions
> but are otherwise like #2 or #3. Transaction control statements are of this
> kind.
>
> If I understand correctly, the existing Pg FUNCTION is essentially #3 and
> the proposed PROCEDURE is essentially #4.
>
Immutable functions are very near to #1. Actually PostgreSQL OUT
parameters are implemented as returned one composite value.
Regards
Pavel
> Maybe I just have to RTFM but I don't know if it is possible now to declare
> a Pg FUNCTION that it stays in the restrictions of #1 or #2. But if not,
> then I think it would be valuable to do so, for assisting reliability and
> performance.
>
> -- Darren Duncan
>
>
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