Durability (ACID) 편집하기

'''Durability''' is one of the four key properties in the [[ACID (Database)|ACID Properties]] of database transactions, ensuring that once a transaction has been committed, its changes are permanently saved in the database. This guarantees that data is not lost even in the event of a system crash, power failure, or hardware malfunction.
==Key Concepts==
*'''Transaction Commit:''' Durability ensures that when a transaction is committed, its effects are persisted.
*'''Non-Volatile Storage:''' Changes made by a committed transaction are saved to non-volatile storage such as a hard drive or SSD.
*'''Crash Recovery:''' Mechanisms like [[Write-Ahead Logging]] (WAL) or checkpoints are used to recover committed transactions after a crash.
==Mechanisms Ensuring Durability==
Several techniques are employed to ensure durability:
#'''Write-Ahead Logging (WAL):'''
#*Ensures that all changes are logged before being applied to the database. Logs are stored in stable storage.
#'''Checkpoints:'''
#*Periodic snapshots of the database state are taken to minimize recovery time in case of a crash.
#'''Redundant Storage:'''
#*Data is replicated across multiple disks or servers to prevent data loss.
#'''Crash Recovery Algorithms:'''
#*Algorithms like [[ARIES]] help recover the database to the last consistent state after a failure.
==Example of Durability==

# A transaction updates a customer's account balance in a banking application. 
# The database writes the update to a log (WAL) before modifying the actual data. 
# The transaction is committed, ensuring the update is stored in non-volatile storage. 
# Even if the system crashes immediately after, the recovery mechanism uses the log to restore the committed transaction.

==Applications==
Durability is critical in systems where data consistency and reliability are paramount:
*'''Banking and Finance:''' Ensures that transactions like money transfers are never lost.
*'''E-Commerce:''' Guarantees that orders and payments are persistently saved.
*'''Healthcare:''' Protects critical patient records from being lost in system failures.
*'''Enterprise Systems:''' Ensures the integrity of business-critical operations.
==Advantages==
*'''Data Integrity:''' Prevents loss of committed data, ensuring database consistency.
*'''Reliability:''' Builds trust in systems handling sensitive or critical information.
*'''Crash Recovery:''' Reduces downtime by enabling automatic recovery.
==Challenges==
*'''Performance Overhead:''' Durability mechanisms like WAL or replication can slow down write operations.
*'''Resource Intensive:''' Requires additional storage and computational resources.
*'''Implementation Complexity:''' Ensuring durability in distributed systems involves intricate protocols.
==Related Concepts and See Also==
*[[ACID Properties]]
*[[Write-Ahead Logging]]
*[[ARIES (Database)]]
*[[Transaction Management]]
*[[Database Recovery]]
*[[Fault Tolerance]]
*[[Checkpointing]]
[[Category:Database]]