PACELC Theorem
PACELC extends CAP: without partitions, trade between latency (L) and consistency (C); with partitions, trade between availability (A) and consistency (C).
Purpose
To refine the CAP trade-off by incorporating the latency-consistency balance during normal (partition-free) operation.
Mechanism
PA/EL (e.g., Cassandra): choose A during partitions, L without them. PC/EC (e.g., Spanner): choose C during partitions, C without them. PC/EL (e.g., PNUTS): a hybrid strategy.
Use cases
- Fine-grained distributed system selection
- Latency-consistency trade-offs
- Database comparison