The motivating example for this seems to be completely broken:
--- Start a transaction
BEGIN
SAVEPOINT active_record_1
--- Look up the account
SELECT * FROM credit_accounts WHERE customer_id = 1
--- Insert the account; this may fail due to a duplicate constraint
INSERT INTO credit_accounts (customer_id) VALUES (1)
--- Abort this by rolling back
ROLLBACK TO active_record_1
--- Retry here: Start a new subtransaction
SAVEPOINT active_record_2
--- Find the newly-created account
SELECT * FROM credit_accounts WHERE customer_id = 1
--- Save the data
RELEASE SAVEPOINT active_record_2
COMMIT
The second SELECT will never see the newly added row because it's still operating against the same snapshot as the outer transaction, so the use of subtransactions is completely pointless?
