Let's assume transaction A runs in
SERIALIZABLE and transaction B runs in a more permissive isolation level, like
READ UNCOMMITTED. Can Transaction A now suffer from any anomaly introduced by transaction B?
The guarantee that any set of concurrent serializable transactions will have the same effect as if they were run one at a time means that if you can demonstrate that a single transaction, as written, will do the right thing when run by itself, you can have confidence that it will do the right thing in any mix of serializable transactions
I found these references in the SQL draft indicating that
SERIALIZABLE transactions will indeed not suffer from any anomaly induced by other isolation level transactions:
CD 9075-1:200x(E) page 27:
The highest isolation level SERIALIZABLE, guarantees serializable execution, meaning that the effect of SQL-transactions that overlap in time is the same as the effect they would have had, had they not overlapped in time.
CD 9075-2:200x(E) page 124:
Changes made to SQL-data or schemas by an SQL-transaction in an SQL-session may be perceived by that SQL-transaction in that same SQL-session, and by other SQL-transactions, or by that same SQL-transaction in other SQL-sessions, at isolation level READ UNCOMMITTED, but cannot be perceived by other SQL- transactions at isolation level READ COMMITTED, REPEATABLE READ, or SERIALIZABLE until the former SQL-transaction terminates with a .
That's the standard. But how do the implementations do in reality? I'm particularly interested in the defined behaviour of Postgres and MySQL.