Databases & Data Storage
Data Availability
Definition
In the context of distributed systems, availability means that the system is able to process requests and provide a response. An available system is one that is responsive, even if some of its nodes are down or it is experiencing a network partition.
Why It Matters
For many user-facing applications, availability is a top priority. Users expect a service to be online and working, even if it means the data they are seeing is slightly out of date.
Contextual Example
In a large, distributed database, if a network failure separates one data center from the others, an "available" system will allow users connected to that data center to continue reading and writing data, even though that data is temporarily out of sync with the rest of the system.
Common Misunderstandings
- This is the "A" in the CAP theorem and the "A" in BASE.
- There is often a trade-off between strong consistency and high availability in distributed systems.