I want to create a schedule batch that will take records from multiple Objects and update a field. The objects for which the batch will run are specified in custom metadata.

I've considered using an Iterable batch, but using that approach would require looping over the custom metadata records and querying for the records of each object. However, running a query inside a loop would exceed governor limits.

Does using an Iterable batch limit the number of records compared to using a database.queryLocator? The database.queryLocator approach allows processing up to 50 million records. What are the limitations with the Iterable approach?

Do you have any other suggestion?