ACID vs CAP
ACID (Atomicity, Consistency, Isolation, Durability) and CAP (Consistency, Availability, Partition tolerance) both come up in technology conversations and get confused. Here's the plain-English difference, side by side, so you can use each one with confidence.
The key difference: ACID refers to atomicity, consistency, isolation, durability, while CAP refers to consistency, availability, partition tolerance — they describe different things even when they show up in the same sentence.
ACID — Atomicity, Consistency, Isolation, Durability
The four guarantees a traditional database transaction provides. ACID is why banks run on Postgres-style systems and not eventually-consistent stores.
CAP — Consistency, Availability, Partition tolerance
Theorem stating a distributed system can guarantee only two of the three properties at once. CAP is the reason every serious system design discussion eventually comes back to trade-offs.
When to use ACID
Reach for "ACID" when the conversation is specifically about atomicity, consistency, isolation, durability. The four guarantees a traditional database transaction provides. ACID is why banks run on Postgres-style systems and not eventually-consistent stores.
When to use CAP
Reach for "CAP" when the conversation is specifically about consistency, availability, partition tolerance. Theorem stating a distributed system can guarantee only two of the three properties at once. CAP is the reason every serious system design discussion eventually comes back to trade-offs.
FAQs
What is the difference between ACID and CAP?
ACID stands for Atomicity, Consistency, Isolation, Durability — The four guarantees a traditional database transaction provides. ACID is why banks run on Postgres-style systems and not eventually-consistent stores. CAP stands for Consistency, Availability, Partition tolerance — Theorem stating a distributed system can guarantee only two of the three properties at once. CAP is the reason every serious system design discussion eventually comes back to trade-offs.
Are ACID and CAP the same thing?
No. They're often used in the same conversation because they're related, but they describe different concepts. ACID = Atomicity, Consistency, Isolation, Durability. CAP = Consistency, Availability, Partition tolerance.
When should I use ACID vs CAP?
Use ACID when you're specifically referring to atomicity, consistency, isolation, durability. Use CAP when the topic is consistency, availability, partition tolerance.