CAP定理は、分散システムが最大で3つのうち2つの特性 — 一貫性(Consistency)、可用性(Availability)、分割耐性(Partition tolerance) — を同時に保証できることを述べています。ネットワーク分割は避けられないため、実際の選択肢は分割中の一貫性と可用性の間になります。
3つの特性
CONSISTENCY (C) → every read sees the latest write (all nodes agree on the data)
AVAILABILITY (A) → every request gets a response (the system stays responsive)
PARTITION TOLERANCE (P) → the system keeps working despite network partitions
(communication breaks between nodes)
→ CAP: you can only fully guarantee TWO of these three simultaneously.
