Horton

Re: Skipping logical replication transactions on subscriber side

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: "osumi.takamichi@fujitsu.com" <osumi.takamichi@fujitsu.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>, "David G. Johnston" <david.g.johnston@gmail.com>, "tanghy.fnst@fujitsu.com" <tanghy.fnst@fujitsu.com>, vignesh C <vignesh21@gmail.com>, Greg Nancarrow <gregn4422@gmail.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, Alexey Lesovsky <lesovsky@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2022-03-16T02:32:31Z
Lists: pgsql-hackers 
On Tue, Mar 15, 2022 at 7:30 PM osumi.takamichi@fujitsu.com
<osumi.takamichi@fujitsu.com> wrote:
>
> On Tuesday, March 15, 2022 3:13 PM Masahiko Sawada <sawada.mshk@gmail.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.

Commits

  1. Test ALIGNOF_DOUBLE==4 compatibility under ALIGNOF_DOUBLE==8.

  2. Reorder subskiplsn in pg_subscription to avoid alignment issues.

  3. Add ALTER SUBSCRIPTION ... SKIP.

  4. Optionally disable subscriptions on error.

  5. Update docs of logical replication for commit 8d74fc96db.

  6. Respect permissions within logical replication.

  7. Fix regression test failure caused by commit 8d74fc96db.

  8. Add a view to show the stats of subscription workers.

  9. Add logical change details to logical replication worker errcontext.

  10. Rename LOGICAL_REP_MSG_STREAM_END to LOGICAL_REP_MSG_STREAM_STOP.

  11. Fix typo in protocol.sgml.

  12. Remove unused argument in apply_handle_commit_internal().

  13. Fix replication of in-progress transactions in tablesync worker.

  14. Reorder pg_sequence columns to avoid alignment issue