In
database system
In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases spa ...
s, durability is the
ACID property which guarantees that
transactions that have committed will survive permanently.
For example, if a flight booking reports that a seat has successfully been booked, then the seat will remain booked even if the system crashes.
Durability can be achieved by flushing the transaction's log records to
non-volatile storage
Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data.
Non-volatile memory typi ...
before acknowledging commitment.
In
distributed transaction A distributed transaction is a database transaction in which two or more network hosts are involved. Usually, hosts provide transactional resources, while the transaction manager is responsible for creating and managing a global transaction that enc ...
s, all participating servers must coordinate before commit can be acknowledged. This is usually done by a
two-phase commit protocol
In transaction processing, databases, and computer networking, the two-phase commit protocol (2PC) is a type of atomic commitment protocol (ACP). It is a distributed algorithm that coordinates all the processes that participate in a distributed ...
.
Many DBMSs implement durability by writing transactions into a
transaction log
In the field of databases in computer science, a transaction log (also transaction journal, database log, binary log or audit trail) is a history of actions executed by a database management system used to guarantee ACID properties over crashes ...
that can be reprocessed to recreate the system state right before any later failure. A transaction is deemed committed only after it is entered in the log.
See also
*
Atomicity
*
Consistency
In classical deductive logic, a consistent theory is one that does not lead to a logical contradiction. The lack of contradiction can be defined in either semantic or syntactic terms. The semantic definition states that a theory is consistent ...
*
Isolation
*
Relational database management system
References
Data management
Transaction processing
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