Record locking
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Record locking is the technique of preventing simultaneous access to data in a database, to prevent inconsistent results.
The classic example is demonstrated by two bank clerks attempting to update the same bank account for two different transactions. Clerk 1 and clerk 2 both retrieve (ie, copy) the account's current balance. Clerk 1 applies one transaction and refiles the new balance. Clerk 2 applies a different transaction and refiles a new balance that obliterates the information saved by clerk 1. The resulting account balance no longer reflects the first transaction.
To prevent inconsistencies created by that kind of unlimited access, the account's record can instead be immediately locked upon being retrieved for any subsequent update. Anyone attempting to retrieve the same record for editing is denied access because of the lock (although, depending on the implementation, they may be able to view the record without editing it). Once the record is saved or edits are canceled, the lock is released, thereby always insuring consistent data within the record being edited.