🧱Durability (ACID)

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Also known as: Fault Tolerance

The ACID guarantee that once a transaction commits, its effects persist despite crashes, power loss, or errors.

DESCRIPTION

Durability ensures committed data survives failures and remains available after recovery. Databases implement durability with write-ahead logging, checkpoints, and reliable storage ordering. Replication and synchronous commit options further strengthen persistence. On restart, recovery replays logs to restore a consistent state. Durability trades off with latency and throughput depending on synchronous vs. asynchronous strategies. In distributed systems, durability interacts with availability and consistency under failure models.

ALTERNATIVE DEFINITIONS

Wikipedia

Durability means that once a transaction has been committed, it will remain so, even in the event of power loss, crashes, or errors.

Classic, concise definition as part of ACID properties.

Source

PostgreSQL

Write-ahead logging (WAL) ensures that the log is written to persistent storage before any changes are applied to the data files, providing the basis for crash recovery.

Explains the core mechanism used to achieve durability.

Source

Microsoft Learn

Once a transaction is committed, SQL Server guarantees that the data modifications are durable, subject to the configured recovery model and logging.

Ties durability to recovery models and logging configuration.

Source

RELATED TERMS

ACID Atomicity Consistency Isolation Transaction Write-Ahead Logging Transaction Log Replication Crash Recovery Journaling

COMPETING TERMS

BASE

RELATIONS

• Broader: ACID

KNOWLEDGE AREAS

Data Storage & Operations Software Engineering Data Management

TARGET AUDIENCE

Data Engineer Software Developer Data Architect Cloud Architect DevOps Engineer

EXTERNAL SOURCES

• Wikipedia - ACID
• PostgreSQL - WAL and crash recovery overview
• MySQL - InnoDB redo log durability
• Google Cloud - Durability via replicated commits

TOP QUESTIONS

Why is Durability (ACID) critical for transactional systems?

It prevents committed data from being lost, ensuring financial, operational, and legal integrity even after crashes or power failures.

Category: Relevancy

How do databases implement Durability (ACID)?

They use write-ahead logs, fsyncs, checkpoints, and recovery routines; some add synchronous replication for stronger guarantees.

Category: HowTo

What is the trade-off for Durability (ACID)?

Stronger durability may increase write latency due to synchronous disk flushes or replication acknowledgments.

Category: Opinion

How does Durability (ACID) relate to BASE systems?

BASE systems prioritize availability and eventual consistency, sometimes relaxing immediate durability for speed and partition tolerance.

Category: Concept

What configuration mistakes undermine Durability (ACID)?

Disabling fsync, storing logs on unreliable media, or misconfigured caches can silently lose committed writes.

Category: Mistakes

Does replication guarantee Durability (ACID)?

Synchronous replication can strengthen durability, while asynchronous replication risks data loss on primary failure before replica catch-up.

Category: Risks

How do cloud services enhance Durability (ACID)?

Managed services often replicate across zones/regions and abstract storage durability via distributed logs and consensus.

Category: Management

What testing validates Durability (ACID)?

Chaos testing with crash/reboot and power-cut simulations verifies recovery restores all committed transactions.

Category: Testing

When might you relax Durability (ACID)?

For high-throughput telemetry where occasional loss is acceptable, buffered or batch writes can trade durability for speed.

Category: Opinion