Re: Skipping logical replication transactions on subscriber side

On Tue, Mar 15, 2022 at 7:30 PM osumi(dot)takamichi(at)fujitsu(dot)com
<osumi(dot)takamichi(at)fujitsu(dot)com> wrote:
>
> On Tuesday, March 15, 2022 3:13 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > I've attached an updated version patch.
>
> A couple of minor comments on v14.
>
> (1) apply_handle_commit_internal
>
>
> + if (is_skipping_changes())
> + {
> + stop_skipping_changes();
> +
> + /*
> + * Start a new transaction to clear the subskipxid, if not started
> + * yet. The transaction is committed below.
> + */
> + if (!IsTransactionState())
> + StartTransactionCommand();
> + }
> +
>
> I suppose we can move this condition check and stop_skipping_changes() call
> to the inside of the block we enter when IsTransactionState() returns true.
>
> As the comment of apply_handle_commit_internal() mentions,
> it's the helper function for apply_handle_commit() and
> apply_handle_stream_commit().
>
> Then, I couldn't think that both callers don't open
> a transaction before the call of apply_handle_commit_internal().
> For applying spooled messages, we call begin_replication_step as well.
>
> I can miss something, but timing when we receive COMMIT message
> without opening a transaction, would be the case of empty transactions
> where the subscription (and its subscription worker) is not interested.
>

I think when we skip non-streamed transactions we don't start a
transaction. So, if we do what you are suggesting, we will miss to
clear the skip_lsn after skipping the transaction.

--
With Regards,
Amit Kapila.