Re: Skip collecting decoded changes of already-aborted transactions

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.

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Commit message

typo /RBTXN_IS_PREAPRE/RBTXN_IS_PREPARE/

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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)

and make appropriate macro changes

e.g.

/* prepare for this transaction skipped? */
#define rbtxn_skip_prepared(txn) \
( \
((txn)->txn_flags & RBTXN_SKIPPED_PREPARE == RBTXN_SKIPPED_PREPARE) \
)

/* Has a prepare or stream_prepare already been sent? */
#define rbtxn_sent_prepare(txn) \
( \
((txn)->txn_flags & RBTXN_SENT_PREPARE == RBTXN_SENT_PREPARE) \
)

Thoughts?

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Kind Regards,
Peter Smith.
Fujitsu Australia