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  1. Doc: minor improvements for plpgsql "Transaction Management" section.

  1. Savepoints in plpgsql

    The Post Office <noreply@postgresql.org> — 2024-07-12T05:52:24Z

    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.

  2. Re: Savepoints in plpgsql

    David G. Johnston <david.g.johnston@gmail.com> — 2024-07-12T13:15:20Z

    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.

  3. Re: Savepoints in plpgsql

    Tom Lane <tgl@sss.pgh.pa.us> — 2024-07-12T13:42:24Z

    "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

  4. Re: Savepoints in plpgsql

    Olleg Samoylov <splarv@ya.ru> — 2024-08-05T08:20:58Z

    
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.
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