Ultimate consistency in distributed systems: how to apply and how to compensate for data inconsistencies?

Deeply discuss the final consistency in distributed systems

In distributed system architecture, distributed transaction processing has always been a difficult problem. In order to solve the consistency problem between sub-transactions, CAP theory and BASE theory are often mentioned, which leads us to choose CP mode (strong consistency) or AP mode (final consistency). The CP pattern is relatively simple, and consistency is usually guaranteed by consolidating multiple transactions into a single transaction. However, the final consistency in the AP mode is more complex, and its application scenarios and implementation methods are more challenging. This article will conduct in-depth analysis of the scenarios and implementation methods of final consistency in practical applications.

Many people are confused about the concept of final consistency in AP mode and want to understand the specific application scenarios and repair strategies in case of data inconsistencies.

In practical applications, scenarios that fully pursue strong consistency (CP) are not common, especially in high-concurrency and high-availability systems. Sacrifice partial consistency in exchange for higher availability is often a better strategy. For example, in scenarios involving fund operations, data consistency must be ensured and any data loss or inconsistency cannot be tolerated, which is more suitable for the CP model.

The AP model, that is, ultimate consistency, has the core idea of ​​allowing the system to have data inconsistencies within a certain period of time, but it will eventually reach a consistent state. For example, user registration: Even if a subsystem registration fails, as long as the main system succeeds, the entire registration process can be considered successful. In the future, other system data can be synchronized through compensation mechanisms (such as timing tasks or message queues) to ultimately achieve data consistency. This reflects the fault tolerance and high availability of the AP model. Of course, this mechanism needs to be carefully designed to ensure consistency of the final data and control inconsistent time windows.

It should be noted that the applicable scenarios of the AP model are limited, and it is necessary to carefully weigh the system's fault tolerance and data consistency requirements. The choice of CP and AP patterns depends on the specific needs of the business for consistency and availability. If data consistency requirements are extremely high, even if part of the availability is sacrificed, you should choose CP mode; if the system requires higher availability and can tolerate short-term data inconsistencies, you can choose AP mode.

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