> For the complete documentation index, see [llms.txt](https://eric-zhang-seattle.gitbook.io/mess-around/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://eric-zhang-seattle.gitbook.io/mess-around/distributed-system-theories/cap.md).

# Elementary school with CAP

* [History](#history)
* [Definition](#definition)
  * [Consistency](#consistency)
  * [Availability](#availability)
  * [Partition tolerance](#partition-tolerance)
* [Use case](#use-case)
* [Limitations](#limitations)
  * [Not choose two from three](#not-choose-two-from-three)
  * [Limited model](#limited-model)
    * [Consistency model](#consistency-model)
    * [Fault tolerant model](#fault-tolerant-model)
* [References](#references)

## History

* Applications don't require linearizability can be more tolerant of network problems (CAP)

## Definition

### Consistency

* Every read would get the most recent write. Actually means linearizability.

### Availability

* Availability: Every request received by the nonfailing node in the system must result in a response.

### Partition tolerance

* Partition tolerance: The cluster can survive communication breakages in the cluster that separate the cluster into multiple partitions unable to communicate with each other.

## Use case

* Simplified theory for elementary distributed system learners.

## Limitations

### Not choose two from three

* Def: Either choose consistency or availability when partitioned.

### Limited model

#### Consistency model

* It only considers one consistency model (namely linearizability)

#### Fault tolerant model

* It only considers one kind of fault (network partitions). It doesn't say anything about network delays, dead nodes, or other trade-offs.

## References

* <https://martin.kleppmann.com/2015/05/11/please-stop-calling-databases-cp-or-ap.html>