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Data & Analytics · Advanced

PACELC Theorem

An extension of CAP: if there is a Partition, choose Availability or Consistency; Else, choose Latency or Consistency.

Definition

PACELC recognizes that even without partitions, replicated systems trade latency against consistency. DynamoDB and Cassandra are PA/EL, while Spanner is PC/EC.

Exam tip

PACELC adds the normal-operation trade-off (latency vs consistency) that CAP ignores.

Related terms