Обсуждение: A question about StartSubTransaction

Hi hackers,

I found the StartSubTransaction has the following code:

    static void
    StartSubTransaction(void)
    {
        [...]

        s->state = TRANS_START;

        /*
         * Initialize subsystems for new subtransaction
         *
         * must initialize resource-management stuff first
         */
        AtSubStart_Memory();
        AtSubStart_ResourceOwner();
        AfterTriggerBeginSubXact();

        s->state = TRANS_INPROGRESS;

        [...]
    }

IIRC, AtSubStart_Memory, AtSubStart_ResourceOwner and AfterTriggerBeginSubXact don't
use s->state.  Why should we set s->state to TRANS_START and then TRANS_INPROGRESS?


-- 
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.

Japin Li <japinli@hotmail.com> writes:
> IIRC, AtSubStart_Memory, AtSubStart_ResourceOwner and AfterTriggerBeginSubXact don't
> use s->state.

No, they don't.

> Why should we set s->state to TRANS_START and then TRANS_INPROGRESS?

I believe it's so that if an error gets thrown somewhere in that
area, we'll recover properly.  I'd be the first to say that this
stuff isn't terribly well-tested, since it's hard to force an
error there.

            regards, tom lane

On Wed, 14 Sep 2022 at 13:52, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Japin Li <japinli@hotmail.com> writes:
>> Why should we set s->state to TRANS_START and then TRANS_INPROGRESS?
>
> I believe it's so that if an error gets thrown somewhere in that
> area, we'll recover properly.  I'd be the first to say that this
> stuff isn't terribly well-tested, since it's hard to force an
> error there.
>

Thanks for the explanation!  Maybe more comments here is better.

-- 
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.