Clickhouse: Schema change in system.tables

[rochoa]

I just realized that the schema of the system.tables table has changed recently (https://github.com/ClickHouse/ClickHouse/pull/6489), the data_path column is gone and a new data_paths column exists now.

This is already in the latest stable releases, but the documentation is not reflecting the new schema, neither is documented in the changelog.

Wouldn't you consider this a breaking/backwards-incompatible change?

[alexey-milovidov]

We don't enforce backward compatibility for system tables. But it should be mentioned in changelog and documentation.

[rochoa]

Understood. Thanks for the clarification.

[abraithwaite]

We don't enforce backward compatibility for system tables. But it should be mentioned in changelog and documentation.

Why? We depend on these tables for operations and system management. It is not a nice experience to have those break suddenly upon upgrade. Even in testing, where we discovered it, it requires additional toil to upgrade unnecessarily.

At the very least, it should not have been missed in the release notes.

[alexey-milovidov]

Ok, we should note all the changes in changelog as "backward incompatible changes".

Regarding the question of "why", we simply do not have practice to keep them backward compatible. Maybe we should.