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Re: Transaction manipulation commands in user defined c functions?

From: Michael Hadjivassiliou <sporegnosis(at)gmail(dot)com>
To: pgsql-novice(at)postgresql(dot)org
Subject: Re: Transaction manipulation commands in user defined c functions?
Date: 2010-06-09 20:24:08
Message-ID: AANLkTinSv9VLLlNLhZjsRg53uE1z7vjG5H3X8Yh9-eY7@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-novice
Unfortunately part of the code must be in c. I could follow a hybrid
approach
by coding the stuff surrounded by the transaction blocks in c functions and
the rest in pl/pgsql,
however that approach is not elegant imho.

I can understand that the c api for managing transactions might change in
the future. r there plans for it to become "standardized" at some point?


>Well, sure.  Look at the way that plpgsql implements a BEGIN/EXCEPTION
>block, for example.  You need to establish a subtransaction and have
>a TRY/CATCH block to catch the error and clean up.

can you suggest some .c files or links to have a look?

Thanks.

On Wed, Jun 9, 2010 at 7:14 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Michael Hadjivassiliou <sporegnosis(at)gmail(dot)com> writes:
> > I've been searching for a way to do transaction blocks and savepoints
> within
> > a user defined c function. Apparently the docs state that if an SPI
> function
> > throws an error, control goes out of the function and the current
> > transaction is rolled back, yet it hints that you can do subtransactions
> > within a c function.
>
> Well, sure.  Look at the way that plpgsql implements a BEGIN/EXCEPTION
> block, for example.  You need to establish a subtransaction and have
> a TRY/CATCH block to catch the error and clean up.
>
> But having said that ... it's pretty messy and I wonder why you are
> wanting to do this in a C function.  Your code would be a lot more
> future-proof in plpgsql, say.  And if you're invoking operations as
> heavyweight as a subtransaction, you're certainly not going to get any
> noticeable performance win from using C.
>
>                        regards, tom lane
>

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