RE: Multi-Master Logical Replication

Hi,

In addition to the use cases mentioned above, some users want to use n-way
replication of partial database.

The following is the typical use case.

* There are several data centers.
(ex. Japan and India)
* The database in each data center has its unique data.
(ex. the database in Japan has the data related to Japan)
* There are some common data.
(ex. the shipment data from Japan to India should be stored on both database)
* To replicate common data, users want to use n-way replication.

The current POC patch seems to support only n-way replication of entire database,
but I think we should support n-way replication of partial database to achieve
above use case.

> I don't know if it requires the kind of code you are thinking but I
> agree that it is worth considering implementing it as an extension.

I think the other advantage to implement as an extension is that users could
install the extension to older Postgres.

As mentioned in previous email, the one use case of n-way replication is migration
from older Postgres to newer Postgres.

If we implement as an extension, users could use n-way replication for migration
from PG10 to PG16.

Regards,
Ryohei Takahashi