Re: Skip collecting decoded changes of already-aborted transactions

On Thu, Jan 23, 2025 at 2:17 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Wed, Jan 22, 2025 at 9:21 AM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
> >
> > On Wed, Jan 22, 2025 at 5:36 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > >
> > > On Sun, Jan 19, 2025 at 7:53 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > > >
> > > > On Fri, Jan 17, 2025 at 11:19 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > > > >
> > > > > On Wed, Jan 15, 2025 at 4:43 PM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
> > > > > >
> > > > > > My thoughts are that any consistency improvement is a step in the
> > > > > > right direction so even "don't increase the consistency much" is still
> > > > > > better than nothing.
> > > > >
> > > > > I agree that doing something is better than nothing. The proposed
> > > > > idea, having RBTXN_IS_PREPARED prefix for all related flags, improves
> > > > > the consistency in terms of names, but I'm not sure this is the right
> > > > > direction. For example, RBTXN_IS_PREPARED_SKIPPED is quite confusing
> > > > > to me. I think this name implies "this is a prepared transaction but
> > > > > is skipped", but I don't think it conveys the meaning well. In
> > > > > addition to that, if we add RBTXN_IS_PREPARED flag also for skipped
> > > > > prepared transactions, we would end up with doing like:
> > > > >
> > > > > txn->txn_flags |= (RBTXN_IS_PREPARED | RBTXN_IS_PREPARED_SKIPPED);
> > > > >
> > > > > Which seems quite redundant. It makes more sense to me to do like:
> > > > >
> > > > > txn->txn_flags |= (RBTXN_IS_PREPARED | RBTXN_SKIPPED_PREPARE);
> > > > >
> > > > > I'd like to avoid a situation like where we rename these names just
> > > > > for better consistency in terms of names and later rename them to
> > > > > better names for other reasons again and again.
> > > > >
> > > >
> > > > Sounds reasonable. We agree with just changing RBTXN_PREPARE to
> > > > RBTXN_IS_PREPARED and its corresponding macro. The next step is to
> > > > update the patch to reflect the same.
> > >
> > > Right. I've attached the updated patches.
> > >
> >
> > Some review comments for v15-0002.
> >
> > ======
> > Commit message
> >
> > typo /RBTXN_IS_PREAPRE/RBTXN_IS_PREPARE/
> >
> > ======
> >
> > I'm not trying to be pedantic, but there seems to be something strange
> > about the combination usage of these PREPARE constants, which raises
> > lots of questions for me...
> >
> > For example.
> > I had thought RBTXN_SKIPPED_PREPARE meant it is a prepared tx AND it is skipped
> > I had thought RBTXN_SENT_PREPARE meant it is a prepared tx AND it is sent
> >
> > So I was surprised that the patch makes this change:
> > - txn->txn_flags |= RBTXN_SKIPPED_PREPARE;
> > + txn->txn_flags |= (RBTXN_IS_PREPARED | RBTXN_SKIPPED_PREPARE);
> >
> > because, if we cannot infer that RBTXN_SKIPPED_PREPARE *must* mean it
> > is a prepared transaction then why does that constant even have
> > "PREPARE" in its name at all instead of just being called
> > RBTXN_SKIPPED?
> >
> > e.g., either of these makes sense to me:
> > txn->txn_flags |= (RBTXN_IS_PREPARED | RBTXN_SKIPPED);
> > txn->txn_flags |= RBTXN_SKIPPED_PREPARE;
> >
> > But this combination seemed odd:
> > txn->txn_flags |= (RBTXN_IS_PREPARED | RBTXN_SKIPPED_PREPARE);
> >
> > Also, this code (below) seems to be treating those macros as
> > unrelated, but IIUC we know that rbtxn_skip_prepared(txn) is not
> > possible unless rbtxn_is_prepared(txn) is true.
> >
> > - if (rbtxn_prepared(txn) || rbtxn_skip_prepared(txn))
> > + if (rbtxn_is_prepared(txn) || rbtxn_skip_prepared(txn))
> > continue;
> >
> > ~~
> >
> > Furthermore, if we cannot infer that RBTXN_SKIPPED_PREPARE *must* also
> > be a prepared transaction, then why aren't the macros changed to match
> > that interpretation?
> >
> > e.g.
> >
> > /* prepare for this transaction skipped? */
> > #define rbtxn_skip_prepared(txn) \
> > ( \
> > ((txn)->txn_flags & RBTXN_IS_PREPARED != 0) && \
> > ((txn)->txn_flags & RBTXN_SKIPPED_PREPARE != 0) \
> > )
> >
> > /* Has a prepare or stream_prepare already been sent? */
> > #define rbtxn_sent_prepare(txn) \
> > ( \
> > ((txn)->txn_flags & RBTXN_IS_PREPARED != 0) && \
> > ((txn)->txn_flags & RBTXN_SENT_PREPARE != 0) \
> > )
> >
> > ~~~
> >
> > I think a to fix all this might be to enforce the RBTXN_IS_PREPARED
> > bitflag is set also for RBTXN_SKIPPED_PREPARE and RBTXN_SENT_PREPARE
> > constants, removing the ambiguity about how exactly to interpret those
> > two constants.
> >
> > e.g. something like
> >
> > #define RBTXN_IS_PREPARED 0x0040
> > #define RBTXN_SKIPPED_PREPARE (0x0080 | RBTXN_IS_PREPARED)
> > #define RBTXN_SENT_PREPARE (0x0200 | RBTXN_IS_PREPARED)
> >
>
> I think the better way would be to ensure that where we set
> RBTXN_SENT_PREPARE or RBTXN_SKIPPED_PREPARE, the transaction is a
> prepared one (RBTXN_IS_PREPARED must be already set). It should be
> already the case for RBTXN_SENT_PREPARE but we can ensure the same for
> RBTXN_SKIPPED_PREPARE as well.
>
> Will that address your concern? Does anyone else have an opinion on this matter?

Yes that would be OK, but should also add some clarifying comments in
the "reorderbuffer.h" like:

#define RBTXN_SKIPPED_PREPARE 0x0080 /* this flag can only be set
for RBTXN_IS_PREPARED transactions */
#define RBTXN_SENT_PREPARE 0x0200 /* this flag can only be set for
RBTXN_IS_PREPARED transactions */

======
Kind Regards,
Peter Smith.
Fujitsu Australia