When a transaction has been open for long enough, it will be considered a slow transaction and we will write a slow transaction log upon commit or an abort. For prepared transactions, we log the prepared duration in the slow transaction logs. If an exception is thrown in prepareTransaction in between setting the transaction state to "prepared" and TransactionMetricsObserver.onPrepare within a slow transaction, then system will crash with an invariant failure in getPreparedDuration since the prepareStartTime was never set to be larger than 0.