Обсуждение: Savepoints in plpgsql
The following documentation comment has been logged on the website: Page: https://www.postgresql.org/docs/16/plpgsql-transactions.html Description: https://www.postgresql.org/docs/current/plpgsql-transactions.html In this section nothing mentioned that a savepoint (a subtransaction) will not work inside plpgsql. Savepoint command is ended with "ERROR: unsupported transaction command in PL/pgSQL". Also need to say, that "begin end" block with "exception" handler will implicitly save and release savepoints.
On Thursday, July 11, 2024, PG Doc comments form <noreply@postgresql.org> wrote:
The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/16/plpgsql-transactions. html
Description:
https://www.postgresql.org/docs/current/plpgsql- transactions.html
In this section nothing mentioned that a savepoint (a subtransaction) will
not work inside plpgsql.
Correct, we prefer to just document how things work. 43.2 does mention that blocks form subtransactions.
Also need to say, that "begin
end" block with "exception" handler will implicitly save and release
savepoints.
A savepoint is an SQL command giving you access to subtransactions. Plpgsql doesn’t need or use it, it has a direct access to subtransactions though in a limited/different way. In short, even if this worked this way we wouldn’t document such an implementation detail.
I suppose we could draw analogies to savepoints, or maybe mention subtransactions again in the procedure transactions chapter. Namely by explaining why the last limitation on that page exists, which I presume is related to subtransactions. But really that page is meant to show how procedures can use commit/rollback to anffect the outer transaction unlike all other plpgsql code which simply gets block-based subtransactions management as previously described. It does this sufficiently and need not be cluttered by subtransaction discussion in any meaningful detail.
David J.
"David G. Johnston" <david.g.johnston@gmail.com> writes:
> On Thursday, July 11, 2024, PG Doc comments form <noreply@postgresql.org>
> wrote:
>> In this section nothing mentioned that a savepoint (a subtransaction) will
>> not work inside plpgsql.
> Correct, we prefer to just document how things work. 43.2 does mention
> that blocks form subtransactions.
It probably would be reasonable to mention something about this
in 43.8, if only to provide an excuse to cross-reference 43.6.8.
I'm imagining more or less
PL/pgSQL does not support savepoints (SAVEPOINT/ROLLBACK TO
SAVEPOINT/RELEASE SAVEPOINT commands). Typical usage patterns
for savepoints can be replaced by blocks with exception handlers
(see 43.6.8).
I also notice the last para
A transaction cannot be ended inside a block with exception handlers.
which seems like it could be tied into that somehow. Maybe eliminate
that as a separate para, and write
PL/pgSQL does not support savepoints (SAVEPOINT/ROLLBACK TO
SAVEPOINT/RELEASE SAVEPOINT commands). Typical usage patterns
for savepoints can be replaced by blocks with exception handlers
(see 43.6.8). Under the hood, a block with exception handlers
forms a subtransaction, which means that transactions cannot
be ended inside such a block.
regards, tom lane
On 12.07.2024 16:42, Tom Lane wrote: > > PL/pgSQL does not support savepoints (SAVEPOINT/ROLLBACK TO > SAVEPOINT/RELEASE SAVEPOINT commands). Typical usage patterns > for savepoints can be replaced by blocks with exception handlers > (see 43.6.8). Under the hood, a block with exception handlers > forms a subtransaction, which means that transactions cannot > be ended inside such a block. > > regards, tom lane Yes, this will be fine. -- Олег