Glossary

Eventual Consistency

Replicas may briefly disagree after a write, but with no new writes they all converge to the same value.

1 min read·4 sections
Open the interactive version → diagrams, practice & more

Definition

Replicas may briefly disagree after a write, but with no new writes they all converge to the same value.

How it works

The price of high availability and low latency in an AP store: a read right after a write might return a stale value from a lagging replica. Good enough for likes, feeds and counters; not for bank balances. Read-your-writes and monotonic-read sessions soften the rough edges.

Common questions

What is Eventual Consistency?

Replicas may briefly disagree after a write, but with no new writes they all converge to the same value.

How does Eventual Consistency work?

The price of high availability and low latency in an AP store: a read right after a write might return a stale value from a lagging replica. Good enough for likes, feeds and counters; not for bank balances. Read-your-writes and monotonic-read sessions soften the rough edges.

What is Eventual Consistency used for in system design?

The price of high availability and low latency in an AP store: a read right after a write might return a stale value from a lagging replica. Good enough for likes, feeds and counters; not for bank balances. Read-your-writes and monotonic-read sessions soften the rough edges.

Part of Glossary on SystemLore — system design explained with 148 deep topics, interactive diagrams, and a build-it-yourself game. Browse the glossary and "X vs Y" comparisons, or build this one →