If the Teradata system crashes, a COLD restart is activated and an online transaction recovery or deferred recovery is started. The only time a deferred recovery is not done is when the operator enters a COLDWAIT restart.
Deferred transaction recovery allows new transactions to come in from the connected hosts. The process of bringing the Teradata system up after a crash causes the locks to be set. If new transactions should attempt to reference the inconsistent data of the to-be-rolled-back transactions, they are blocked until the recovery process restores the data and releases the lock.