$Durability

A transaction must transform the database from one consistent state to another consistent state.

Nov 18, 2025

Durability guarantees that once a transaction is committed, it stays committed—even if the system crashes immediately after.

Committed = Permanent

Even if there’s a:

• Power outage
• System crash
• Hardware failure
• Software bug

…your data survives.

Databases use persistent storage (disks/SSDs) and techniques like:

• Write-ahead logging (WAL): Recording changes before applying them
• Transaction logs: Keeping a history for recovery
• Checkpointing: Periodically syncing memory to disk

Durability gives users confidence that their transactions won’t vanish into thin air.

There’s a performance cost, writing to disk is slower than memory, but reliability demands it.

Consistency vs Atomicity

They’re complementary. Atomicity gives you clean transactions, durability makes them permanent.

Further Reading

• Designing Data-Intensive Applications