#📝 Note: Consistency Models

#Overview

Consistency models define the rules for how data updates are perceived by different nodes in a distributed system.

#Key Models

• Strong Consistency: After an update, all subsequent reads return the updated value.
• Eventual Consistency: If no new updates are made, eventually all reads will return the last updated value.
• Read-Your-Writes Consistency: A process that updates a record will always see the updated value in subsequent reads.
• Monotonic Reads: If a process has seen a value, it will never see an older value in subsequent reads.

#PACELC Theorem

An extension of the CAP theorem.

• If there is a Partition: trade-off between Availability and Consistency.
• Else (no partition): trade-off between Latency and Consistency.

#When to Choose

• Strong: Financial systems, inventory (to prevent overselling).
• Eventual: Social media feeds, product reviews, search indices.