- Any distributed data store can only provide two of the following three guarantees:
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Consistency (C): All nodes can see the same data at the same time.
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Availability (A): Every request receives a (non-error) response, without the guarantee that it contains the most recent write.
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Partition tolerance (P): The system continues to work despite message loss or partial failure.
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| Combination | Property set | Behavior when a network partition failure happens |
|---|---|---|
| CP (Consistency over Availability) | ACID | The system will return an error or a time out if particular information cannot be guaranteed to be up to date. |
| AP (Availability over Consistency) | BASE | The system will always try to return the most recent available version of the information, but the information cannot be guaranteed to be up to date. |
| CA (This is possible) |
Note: The choice is between consistency and availability only when a network partition or failure happens. When there is no network failure, both availability and consistency can be satisfied.