Snapshot failing due to concurrent schema change [DBZ-2148]

Migrated from [DBZ-2148](https://issues.redhat.com/browse/DBZ-2148)

Running the tutorial example, I was executing a schema change ({{ALTER TABLE customers ADD COLUMN middle_name VARCHAR (255)}}, followed by {{ALTER TABLE customers DROP COLUMN middle_name}}) while starting the MySQL connector. The snapshot failed with this exception:

{quote}
... See original issue ...
{quote}

I'm rather puzzled why this is happening. Maybe we don't open up the snapshot transaction with the right isolation level?

Start with the tutorial example and the MySQL connector snapshot path, reproducing the failure while applying the reported ALTER TABLE statements. Trace the snapshot behavior around the concurrent schema change and use the reported exception to identify the affected path; done means the snapshot completes reliably or the failure is covered by a focused regression test.

Written by the indexing model from the issue text.