Although this chapter has emphasized the recovery of transactions, recovery techniques also apply to the database and to the system after some type of critical error has occurred. Critical events can cause a database to stop working and compromise the integrity of the data. Examples of critical events are:Hardware$/$software failures. A failure of this type could be a hard disk media failure, a bad capacitor on a motherboard, or a failing memory bank. Other causes of errors under this category include application program or operating system errors that cause data to be overwritten, deleted, or lost. Some database administrators argue that this is one of the most common sources of database problems.Human$-$caused incidents. This type of event can be categorized as unintentional or intentional.An unintentional failure is caused by a careless end user. Such errors include deleting the wrong rows from a table, pressing the wrong key on the keyboard, or shutting down the main database server by accident.Intentional events are of a more severe nature and normally indicate that the company data is at serious risk. Under this category are security threats caused by hackers trying to gain unauthorized access to data resources and virus attacks caused by disgruntled employees trying to compromise the database operation and damage the company.Natural disasters. This category includes fires, earthquakes, floods, and power failures.Whatever the cause, a critical error can render the database into an inconsistent state. The following section introduces the various techniques used to recover the database from an inconsistent state to a consistent stat