Re: Skipping logical replication transactions on subscriber side

On Mon, Jan 17, 2022 at 9:35 PM osumi(dot)takamichi(at)fujitsu(dot)com
<osumi(dot)takamichi(at)fujitsu(dot)com> wrote:
>
> On Monday, January 17, 2022 5:03 PM I wrote:
> > Hi, thank you for sharing a new patch.
> > Few comments on the v6.
> >
> > (1) doc/src/sgml/ref/alter_subscription.sgml
> >
> > + resort. This option has no effect on the transaction that is
> > + already
> >
> > One TAB exists between "resort" and "This".
> >
> > (2) Minor improvement suggestion of comment in
> > src/backend/replication/logical/worker.c
> >
> > + * reset during that. Also, we don't skip receiving the changes in
> > + streaming
> > + * cases, since we decide whether or not to skip applying the changes
> > + when
> >
> > I sugguest that you don't use 'streaming cases', because what "streaming
> > cases" means sounds a bit broader than actual your implementation.
> > We do skip transaction of streaming cases but not during the spooling phase,
> > right ?
> >
> > I suggest below.
> >
> > "We don't skip receiving the changes at the phase to spool streaming
> > transactions"
> >
> > (3) in the comment of apply_handle_prepare_internal, two full-width
> > characters.
> >
> > 3-1
> > + * won’t be resent in a case where the server crashes between them.
> >
> > 3-2
> > + * COMMIT PREPARED or ROLLBACK PREPARED. But that’s okay
> > because this
> >
> > You have full-width characters for "won't" and "that's".
> > Could you please check ?
> >
> >
> > (4) typo
> >
> > + * the subscription if hte user has specified skip_xid. Once we start
> > + skipping
> >
> > "hte" should "the" ?
> >
> > (5)
> >
> > I can miss something here but, in one of the past discussions, there seems a
> > consensus that if the user specifies XID of a subtransaction, it would be better
> > to skip only the subtransaction.
> >
> > This time, is it out of the range of the patch ?
> > If so, I suggest you include some description about it either in the commit
> > message or around codes related to it.
> >
> > (6)
> >
> > I feel it's a better idea to include a test whether to skip aborted streaming
> > transaction clears the XID in the TAP test for this feature, in a sense to cover
> > various new code paths. Did you have any special reason to omit the case ?
> >
> > (7)
> >
> > I want more explanation for the reason to restart the subscriber in the TAP test
> > because this is not mandatory operation.
> > (We can pass the TAP tests without this restart)
> >
> > From :
> > # Restart the subscriber node to restart logical replication with no interval
> >
> > IIUC, below would be better.
> >
> > To :
> > # As an optimization to finish tests earlier, restart the subscriber with no
> > interval, # rather than waiting for new error to laucher a new apply worker.
> Few more minor comments

Thank you for the comments!

>
> (8) another full-width char in apply_handle_commit_prepared
>
>
> + * PREPARED won't be resent but subskipxid is left.
>
> Kindly check "won't" ?

Again, I don't follow what you mean by full-width character in this context.

>
> (9) the header comments of clear_subscription_skip_xid
>
> +/* clear subskipxid of pg_subscription catalog */
>
> Should start with an upper letter ?

Okay, I'll change it.

>
> (10) some variable declarations and initialization of clear_subscription_skip_xid
>
> There's no harm in moving below codes into a condition case
> where the user didn't change the subskipxid before
> apply worker clearing it.
>
> + bool nulls[Natts_pg_subscription];
> + bool replaces[Natts_pg_subscription];
> + Datum values[Natts_pg_subscription];
> +
> + memset(values, 0, sizeof(values));
> + memset(nulls, false, sizeof(nulls));
> + memset(replaces, false, sizeof(replaces));
>

Will move.

Regards,

--
Masahiko Sawada
EDB: https://www.enterprisedb.com/