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Today, I will talk to you about how to analyze CAP theory, which may not be well understood by many people. In order to make you understand better, the editor has summarized the following contents for you. I hope you can get something according to this article.

What is CAP Theory?

In computer science theory, CAP Theorem (also known as Brewer Theorem) is proposed by computer scientist Eric Brewer, that is, distributed computer systems cannot provide all three guarantees at the same time:

Consistency: all nodes see the same data at the same time

Availability (Availability): whether successful or not, ensure that every request receives a response

Partition fault tolerance (Partition tolerance): after any partition, the system can still operate in the event of network failure.

Why can CAP only choose two out of three?

The following examples illustrate why CAP can only choose two out of three.

There are N1 and N2 nodes in a network. They all share block V, which has a value of V0. Program A running on N1 can be considered safe, bug-free, predictable and reliable. Running in N2 is a B program. In this example, A will write the new value of V, while B will read the value from V.

The system is expected to do the following

First write a new value of V, V1.

Then the message (M) updates the copy of V from N1 to N2

Now, reading from B will return V1

If the network is partitioned, when the message from N1 to N2 cannot be delivered, performing the third step above will show that although N2 can access the value of V (availability), it is actually inconsistent with the value of V of N1 (consistency).

Meaning

In the system architecture, CAP should be weighed against specific business scenarios. For example, for most Internet applications (such as portals), because of the large number of machines, scattered deployment nodes, network failure is normal, availability must be guaranteed, so only abandon consistency to ensure the AP of the service. For scenarios such as banks that need to ensure consistency, there is usually a tradeoff between the CA and CP models. The CA model is completely unavailable in the event of a network failure, and the CP model has partial availability.

After reading the above, do you have any further understanding of how to analyze CAP theory? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

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