My main concern is to break a scenario that was previously working (14 -> 15) but after a subscriber upgrade
it won't (14 -> 16).
Fair concern. Some cases that might break the logical replication with version upgrade would be:
1- Usage of different binary formats between publisher and subscriber. As stated here [1], binary format has been changed after v7.4.
But I don't think this would be a concern, since we wouldn't even have logical replication with 7.4 and earlier versions.
2- Lack (or mismatch) of binary send/receive functions for custom data types would cause failures. This case can already cause failures with current logical replication, regardless of binary copy. Stated here [2].
3- Copying in binary format would work with the same schemas. Currently, logical replication does not require the exact same schemas in publisher and subscriber.
This is an additional restriction that comes with the COPY command.
If a logical replication has been set up with different schemas and subscription is created with the binary option, then yes this would break things.
This restriction can be clearly stated and wouldn't be unexpected though.
I'm also okay with allowing binary copy only for v16 or later, if you think it would be safer and no one disagrees with that.
What are your thoughts?
I would say that you should test some scenarios:
014_binary.pl and also custom data types, same column with different data
types, etc.
I added scenarios in two tests to test binary copy:
014_binary.pl: This was already testing subscriptions with binary option enabled. I added an extra step to insert initial data before creating the subscription.
So that we can test initial table sync with binary copy.
002_types.pl: This file was already testing more complex data types. I added an extra subscriber node to create a subscription with binary option enabled.
This way, it now tests binary copy with different custom types.
Do you think these would be enough in terms of testing?
Attached patch also includes some additions to the doc along with the tests.
Thanks,
Melih
