Re: Support logical replication of DDLs

On Wed, Mar 29, 2023 at 2:49 AM Zheng Li <zhengli10(at)gmail(dot)com> wrote:
>
>
> I agree that a full fledged DDL deparser and DDL replication is too
> big of a task for one patch. I think we may consider approaching this
> feature in the following ways:
> 1. Phased development and testing as discussed in other emails.
> Probably support table commands first (as they are the most common
> DDLs), then the other commands in multiple phases.
> 2. Provide a subscription option to receive the DDL change, raise a
> notice and to skip applying the change. The users can listen to the
> DDL notice and implement application logic to apply the change if
> needed. The idea is we can start gathering user feedback by providing
> a somewhat useful feature (compared to doing nothing about DDLs), but
> also avoid heading straight into the potential footgun situation
> caused by automatically applying any mal-formatted DDLs.
>

Doesn't this mean that we still need to support deparsing of such DDLs
which is what I think we don't want?

> 3. As cross-version DDL syntax differences are expected to be uncommon
> (in real workload), maybe we can think about other options to handle
> such edge cases instead of fully automating it? For example, what
> about letting the user specify how a DDL should be replicated on the
> subscriber by explicitly providing two versions of DDL commands in
> some way?
>

As we are discussing in another related thread [1], if
publisher_version > subscriber_version then it may not be possible to
form a DDL at publisher which can be applied to the subscriber. OTOH,
we need to think if there could be any problems with publisher_version
< subscriber_version setup, and if so, what we want to do for it.
Once, we have a clear answer to that then I think we will be in a
better position to answer your question.

[1] - https://www.postgresql.org/message-id/OS0PR01MB5716088E497BDCBCED7FC3DA94849%40OS0PR01MB5716.jpnprd01.prod.outlook.com

--
With Regards,
Amit Kapila.