Re: Transaction Question

It would be nice if nested transactions could be (optionally) decoupled
from their enclosing transaction.

John

Manfred Koizar said:
> On Wed, 3 Dec 2003 08:08:49 -0000 (GMT), "John Sidney-Woollett"
> <johnsw@wardbrook.com> wrote:
>>Issue - nested transactions
>
>>This is an issue for us because some procedures make use of a function
>>which issues a row level lock on a table (select ... for update) in order
>>to read and then update a counter, and which then commits to release the
>>lock. The nested function returns the new counter value on return.
>
> AFAICS nested transactions - at least in the way we plan to implement
> them - won't help, because subtransaction commit will not release locks.
> We see a subtransaction as part of the main transaction.  If a
> subtransaction commits but the main transaction aborts, the
> subtransaction's effects are rolled back.
>
>     START TRANSACTION;   -- main xact
>     ...
>     START TRANSACTION;   -- sub xact
>     UPDATE t SET n=n+1 WHERE i=42;
>
> This locks the row with i=42, because if another transaction wants to
> update this row, it cannot know whether to start with the old or the new
> value of n before our transaction commits or rolls back.
>
>     COMMIT;              --sub xact
>
> Here we are still in the main transaction.  Nothing has changed for
> other backends, because they still don't know whether our main
> transaction will succeed or fail.  So we have to keep the lock...
>
>>Is there a simple/elegant solution to this problem?
>
> Perhaps dblink?  Just a thought, I don't have any personal experience
> with it.
>
> Servus
>  Manfred
>
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