[SalesForce] Query for records modified last 15 minutes

generally sysModStamp is sent when the row gets written to the db, but with triggers, workflow etc, there's no real way to generalize when it gets set vs the lifetime of the transaction. Its definitely never going to be transaction commit time.

If you use getUpdated() to do this, part of the response data is the timestamp of the start of the oldest inflight transaction, you can use this as the start time of your next poll. Otherwise, as you say, you can get holes due to the difference between when the sysModStamp is calculated vs when the transaction actually commits.

If you're doing anything remotely expensive on the receiving side, you'll want to have something that double checks the last sysModstamp you processed for each row to help cut down duplicate processing.

If you run test methods, and don't opt to preserve sequencing (it's in the test running page under the options button), any tests you run will cause gaps. Also, failed transactions can cause gaps unless you enable the anti-gap function available by contacting support.