Hi Ryan, On 6/23/2015 12:20 PM, Ryan Culpepper wrote:
Yes, that should be fine. One note about your sample code: the isolation mode of inner transactions must be #f (the default); you can't change isolation levels once you've started an outer transaction. Also keep in mind that nested transactions are not supported for ODBC connections.
Yes, I saw in reading some more that both call-with-transaction and start-transaction create a savepoint if an outer transaction is open. Savepoints are very nice but they don't handle every situation - sometimes you really need a full subtransaction.
Using savepoints means, e.g., that if I need serialize isolation anywhere, I have to use serilize isolation everywhere. For many situations, that's hitting a fly with a sledgehammer and severely impacts performance. There are lots of cases where you need to serialize a particular operation inside a much larger transaction that mostly can run with lower isolation.
[He asks naively not having looked at the code:] Would it be hard to keep savepoint creation if #:isolation is #f but allow other settings to create a real subtransaction? At least if #:isolation is 'serialized? I can't think of any realistic case where a subtransaction would require higher isolation but not need to be serialized.
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