Re: SUBTRANS: Minimizing calls to SubTransSetParent()

On Thu, 15 Sept 2022 at 12:36, Japin Li <japinli@hotmail.com> wrote:
>
>
> On Thu, 15 Sep 2022 at 18:04, Simon Riggs <simon.riggs@enterprisedb.com> wrote:
> > On Wed, 14 Sept 2022 at 15:21, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> >>
> >> On 2022-Aug-30, Simon Riggs wrote:
> >>
> >> > 001_new_isolation_tests_for_subxids.v3.patch
> >> > Adds new test cases to master without adding any new code, specifically
> >> > addressing the two areas of code that are not tested by existing tests.
> >> > This gives us a baseline from which we can do test driven development.
> >> > I'm hoping this can be reviewed and committed fairly smoothly.
> >>
> >> I gave this a quick run to confirm the claimed increase of coverage.  It
> >> checks out, so pushed.
> >
> > Thank you.
> >
> > So now we just have the main part of the patch, reattached here for
> > the auto patch tester's benefit.
>
> Hi Simon,
>
> Thanks for the updated patch, here are some comments.

Thanks for your comments.

> There is a typo, s/SubTransGetTopMostTransaction/SubTransGetTopmostTransaction/g.
>
> +                *    call SubTransGetTopMostTransaction() if that xact overflowed;
>
>
> Is there a punctuation mark missing on the following first line?
>
> +                * 2. When IsolationIsSerializable() we sometimes need to access topxid
> +                *    This occurs only when SERIALIZABLE is requested by app user.
>
>
> When we use function name in comments, some places we use parentheses,
> but others do not use it. Why? I think, we should keep them consistent,
> at least in the same commit.
>
> +                * 3. When TransactionIdSetTreeStatus will use a status of SUB_COMMITTED,
> +                *    which then requires us to consult subtrans to find parent, which
> +                *    is needed to avoid race condition. In this case we ask Clog/Xact
> +                *    module if TransactionIdsAreOnSameXactPage(). Since we start a new
> +                *    clog page every 32000 xids, this is usually <<1% of subxids.

I've reworded those comments, hoping to address all of your above points.

> Maybe we declaration a topxid to avoid calling GetTopTransactionId()
> twice when we should set subtrans parent?
>
> +               TransactionId subxid = XidFromFullTransactionId(s->fullTransactionId);
> +               TransactionId topxid = GetTopTransactionId();
>   ...
> +               if (MyProc->subxidStatus.overflowed ||
> +                       IsolationIsSerializable() ||
> +                       !TransactionIdsAreOnSameXactPage(topxid, subxid))
> +               {
>   ...
> +                       SubTransSetParent(subxid, topxid);
> +               }

Seems a minor point, but I've done this anyway.

Thanks for the review.

v10 attached

--
Simon Riggs                http://www.EnterpriseDB.com/