What is server cache? Detailed explanation of core concepts and principles

at the moment of high-speed operation of Internet applications, users have higher and higher requirements for page loading speed and service response efficiency, and server caching is one of the key technologies to support high-performance services. Many people have heard of its name, but they have little understanding of its specific logic and role scenarios. This article will expand from the core concepts, operating principles, deployment strategies and other dimensions to take you to a comprehensive understanding of server caching and understand how it reduces the burden on the system and speeds up the user.

First, the core concept and classification of server cache?

to understand the value of server caching, it is first necessary to clarify its essence, and different types of server caching application scenarios.

1, the core definition of server cache

server cache refers to the hot data, static resources or calculation results processed by the server, temporarily stored in the medium with faster read and write speed, when the user initiates the same request again, the result is returned directly from the cache medium, without repeating complex database queries, file reading or calculation logic, in order to shorten response time and reduce server load.

2, common classification of server cache

according to the storage location and the role of the object, the server cache can be divided into a variety of types: First, memory cache, such as Redis, Memcached, directly store the data in the server memory, the fastest read and write speed, suitable for storing high-frequency access to small data; Second, disk cache, such as Nginx static resource cache, static files such as pictures, CSS, JS stored in the specified directory of the server disk, reduce the pressure on the back-end service; Third, application-level cache, implemented by the application itself, such as Java in Guava Cache, for specific business logic calculation results cache.

Second, the core function of the server cache principle?

The reason why the

server cache can greatly improve the performance is that its operating mechanism perfectly fits the access law of Internet applications, and we can disassemble its principle through the request processing flow.

1, cache hit processing flow

when a user initiates a request, the server will first check whether there is a corresponding valid data in the server cache. If the cache hits and the data has not expired, the server will directly read the data from the cache medium and return it to the user. The whole process skips the time-consuming steps such as back-end database query and business logic calculation, and the response time can usually be shortened by more than 90%.

2, the processing flow of cache misses

if there is no corresponding data in the cache, or the data has expired, the server will perform the complete business logic: read the original data source from the database, perform calculation processing, and then cache the processed result writing service, and return it to the user at the same time. When the same request arrives later, it can directly hit the cache to avoid repeating time-consuming operations. In addition, the server cache will also ensure the validity of the data through expiration policies and elimination policies, such as setting the TTL expiration time, or using the LRU algorithm to eliminate the most unused cached data.

3. The actual value and application scenarios of server cache?

understand the concept and principle of server cache, let's see what specific role it can play in actual business, and suitable for deployment scenarios.

1, the core value of server cache

the first is to improve the user experience, the server cache can make the page loading speed from a few seconds to hundreds of milliseconds or even tens of milliseconds, to avoid the user waiting for too long and loss; followed by reducing the cost of the server, reducing the number of database queries and CPU calculation amount, a single server can support more user requests, without blind expansion of hardware; finally, to enhance system stability, in the peak traffic period, the server cache can undertake most of the hot requests, to avoid the back-end database due to excessive pressure and collapse.

2, typical application scenarios of server cache

The application scenarios of

server cache are very extensive: such as the product list and product details page of the e-commerce platform, which have high traffic and relatively low update frequency, and are suitable for server cache storage; the hot articles and static resources of news and information websites can be quickly returned to the user through disk cache or CDN cache; and the calculation results of the API interface, such as the user's integral data and ranking information, can greatly reduce the interface response time through memory cache.

Fourth, server cache deployment and maintenance precautions?

to maximize the value of server caching, you need to avoid some common misunderstandings and follow scientific strategies during deployment and maintenance.

1, server cache deployment strategy

deploy the server cache, first of all to choose the appropriate cache type, such as high-frequency small data selected Redis, static resources selected Nginx disk cache; secondly, to set a reasonable cache expiration time, low real-time requirements for data can be set longer expiration time, high real-time data is set for a short time, or take the initiative to update the cache; but also pay attention to cache granularity, avoid cache too large or too small data set, to ensure the reuse of the cache.

2, server cache maintenance points

maintenance server cache, to focus on cache consistency issues, when the original data source update, to clean up or update the corresponding cache in time to avoid the user to obtain expired data; at the same time to monitor the cache hit rate, the hit rate is too low to explain the cache strategy is unreasonable, you need to adjust the cache storage content or expiration time; in addition, but also to do a good job of cache fault-tolerant processing, such as when the cache server is down, the system should be able to automatically downgrade to direct access to the backend, to avoid service interruption.

To sum up, server cache is the core technology to optimize the performance of Internet applications. From the core concept to the operating principle, from the value scenario to the deployment and maintenance, each link determines its actual effect. Reasonable use of server cache can not only improve the user experience, but also reduce the operation and maintenance costs, and enhance the stability of the system. It is an indispensable key component in the modern internet service architecture.