create table from source: source limits are not applied

[nrainer-materialize]

What version of Materialize are you using?

e8e67370fc

What is the issue?

Given

$ postgres-execute connection=mz_system
ALTER SYSTEM SET max_sources = 2
ALTER SYSTEM SET max_tables = 2

> CREATE SOURCE mz_source FROM POSTGRES CONNECTION pg (PUBLICATION 'mz_source');
> CREATE SOURCE mz_source2 FROM POSTGRES CONNECTION pg (PUBLICATION 'mz_source');

the statement

> CREATE SOURCE mz_source3 FROM POSTGRES CONNECTION pg (PUBLICATION 'mz_source');

should fail with "creating source would violate max_sources limit (desired: 3, limit: 2, current: 0)" but does not.

[rjobanp]

@nrainer-materialize I don't know that this is an issue, or at least it's working as desired based on the current implementation:

The limit on sources actually appears to be a limit on the number of 'persist-shards' in-use by a source: https://github.com/MaterializeInc/materialize/blob/598b74acaaa574b7dd63c576a3fc5f35ae0c8c92/src/adapter/src/coord/ddl.rs#L1562-L1577

The limitation uses this method to determine how many 'persist shards' are actually needed by a given source: https://github.com/MaterializeInc/materialize/blob/598b74acaaa574b7dd63c576a3fc5f35ae0c8c92/src/catalog/src/memory/objects.rs#L793-L832

Given that the CREATE SOURCE mz_source FROM POSTGRES CONNECTION pg (PUBLICATION 'mz_source'); statement does not create any subsources, there are no data shards being created for the statement, such that it doesn't affect the overall limit.

If we want to make this limit sources based on the number of source-statements, then we would have to change this logic, but since I did not implement or design the original behavior I am not sure that is something we want. @morsapaes do you have an opinion on this?