I don't think the schema **can** change while a prepared query is being stepped. If it could, I think that would violate several promises made at the library interface. Further, and in support of those promises, whether made explicit therein or not, prepared statements execute within a transaction. Even if the schema were to change *for other connections*, it would not affect the results of a query or DML statement. BTW, I read your "only if it is the first step" as "only if no stepping has begun".