Re: Add macros for ReorderBufferTXN toptxn - Mailing list pgsql-hackers

On Tue, 14 Mar 2023 at 12:37, Peter Smith <smithpb2250@gmail.com> wrote:
>
> Thanks for the review!
>
> On Mon, Mar 13, 2023 at 6:19 PM vignesh C <vignesh21@gmail.com> wrote:
> ...
> > Few comments:
> > 1) Can we move the macros along with the other macros present in this
> > file, just above this structure, similar to the macros added for
> > txn_flags:
> >         /* Toplevel transaction for this subxact (NULL for top-level). */
> > +#define isa_toptxn(rbtxn) (rbtxn->toptxn == NULL)
> > +#define isa_subtxn(rbtxn) (rbtxn->toptxn != NULL)
> > +#define get_toptxn(rbtxn) (isa_subtxn(rbtxn) ? rbtxn->toptxn : rbtxn)
> >
> > 2) The macro name can be changed to rbtxn_is_toptxn, rbtxn_is_subtxn
> > and rbtxn_get_toptxn to keep it consistent with others:
> >         /* Toplevel transaction for this subxact (NULL for top-level). */
> > +#define isa_toptxn(rbtxn) (rbtxn->toptxn == NULL)
> > +#define isa_subtxn(rbtxn) (rbtxn->toptxn != NULL)
> > +#define get_toptxn(rbtxn) (isa_subtxn(rbtxn) ? rbtxn->toptxn : rbtxn)
> >
> > 3) We could add separate comments for each of the macros:
> >         /* Toplevel transaction for this subxact (NULL for top-level). */
> > +#define isa_toptxn(rbtxn) (rbtxn->toptxn == NULL)
> > +#define isa_subtxn(rbtxn) (rbtxn->toptxn != NULL)
> > +#define get_toptxn(rbtxn) (isa_subtxn(rbtxn) ? rbtxn->toptxn : rbtxn)
> >
>
> All the above are fixed as suggested.
>
> > 4) We check if txn->toptxn is not null twice here both in if condition
> > and in the assignment, we could retain the assignment operation as
> > earlier to remove the 2nd check:
> > -       if (txn->toptxn)
> > -               txn = txn->toptxn;
> > +       if (isa_subtxn(txn))
> > +               txn = get_toptxn(txn);
> >
> > We could avoid one check again by:
> > +       if (isa_subtxn(txn))
> > +               txn = txn->toptxn;
> >
>
> Yeah, that is true, but I chose not to keep the original assignment in
> this case mainly because then it is consistent with the other changed
> code ---  e.g. Every other direct member assignment/access of the
> 'toptxn' member now hides behind the macros so I did not want this
> single place to be the odd one out. TBH, I don't think 1 extra check
> is of any significance, but it is not a problem to change like you
> suggested if other people also want it done that way.

The same issue exists here too:
1)
-       if (toptxn != NULL && !rbtxn_has_catalog_changes(toptxn))
+       if (rbtxn_is_subtxn(txn))
        {
-               toptxn->txn_flags |= RBTXN_HAS_CATALOG_CHANGES;
-               dclist_push_tail(&rb->catchange_txns, &toptxn->catchange_node);
+               ReorderBufferTXN *toptxn = rbtxn_get_toptxn(txn);

2)
 -       if (change->txn->toptxn)
-               topxid = change->txn->toptxn->xid;
+       if (rbtxn_is_subtxn(change->txn))
+               topxid = rbtxn_get_toptxn(change->txn)->xid;

If you plan to fix, bothe the above also should be handled.

3) The comment on top of rbtxn_get_toptxn could be kept similar in
both the below places. I know it is not because of your change, but
since it is a very small change probably we could include it along
with this patch:
@@ -717,10 +717,7 @@ ReorderBufferProcessPartialChange(ReorderBuffer
*rb, ReorderBufferTXN *txn,
                return;

        /* Get the top transaction. */
-       if (txn->toptxn != NULL)
-               toptxn = txn->toptxn;
-       else
-               toptxn = txn;
+       toptxn = rbtxn_get_toptxn(txn);

        /*
         * Indicate a partial change for toast inserts.  The change will be
@@ -812,10 +809,7 @@ ReorderBufferQueueChange(ReorderBuffer *rb,
TransactionId xid, XLogRecPtr lsn,
                ReorderBufferTXN *toptxn;

                /* get the top transaction */
-               if (txn->toptxn != NULL)
-                       toptxn = txn->toptxn;
-               else
-                       toptxn = txn;
+               toptxn = rbtxn_get_toptxn(txn);

Regards,
Vignesh