What are some ways to solve high concurrency in Java?

Java methods to solve high concurrency: 1. HTML static method to avoid a large number of database access requests; 2. Image server separation method; 3. Database cluster and library table hashing method; 4. Load balancing , hardware four-layer switching and software four-layer switching method.

Java's method to solve high concurrency:

1. HTML staticization

In fact, everyone knows that the most efficient and least consumed is a purely static html page, so we try our best to use static pages for the pages on our website. This simplest method is actually the most effective. method.

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But for For websites with a large amount of content and frequent updates, we cannot implement them all manually one by one, so our common information publishing system CMS appeared, such as the news channels of various portal sites we often visit, and even their other channels , are managed and implemented through the information release system. The information release system can realize the simplest information entry and automatically generate static pages. It can also have functions such as channel management, permission management, and automatic crawling. For a large website, Having an efficient and manageable CMS is essential.

In addition to portals and information publishing type websites, for community type websites with high interactivity requirements, being as static as possible is also a necessary means to improve performance. Posts and articles in the community can be processed in real time. Staticization, and then re-staticizing when there is an update, is also a widely used strategy. Mop's hodgepodge uses this strategy, as does the NetEase community and so on.

At the same time, html staticization is also a means used by some caching strategies. For applications in the system that frequently use database queries but have very small content updates, you can consider using html staticization, such as public forums in forums. Setting information, this information can be managed by the current mainstream forums and stored in the database. In fact, a large number of this information is called by the front-end program, but the update frequency is very small. You can consider making this part of the content static when updating the background. This avoids a large number of database access requests.

2. Image server separation

As we all know, for web servers, whether it is Apache, IIS or other containers, images consume the most resources, so we It is necessary to separate images from pages. This is a strategy basically adopted by large websites. They all have independent image servers, or even many image servers.

Such an architecture can reduce the pressure on the server system that provides page access requests, and can ensure that the system will not crash due to picture problems. Different configuration optimizations can be performed on the application server and picture server, such as apache in When configuring ContentType, you can support as few LoadModules as possible to ensure higher system consumption and execution efficiency.

3. Database cluster and database table hashing

Large websites have complex applications, and these applications must use databases. When faced with a large number of accesses, The bottleneck of the database will soon appear. At this time, one database will soon be unable to meet the application, so we need to use database clustering or database table hashing.

In terms of database clusters, many databases have their own solutions. Oracle, Sybase, etc. have good solutions. The commonly used Master/Slave provided by MySQL is also a similar solution. What kind of DB do you use? Just refer to the corresponding solution to implement it.

4. Caching

Anyone who is involved in technology has been exposed to the word cache, and cache is used in many places. Caching in website architecture and website development is also very important. Here we first talk about the two most basic caches. Advanced and distributed caching are described later.

Architecture-wise caching, anyone familiar with Apache will know that Apache provides its own cache module, and you can also use the additional Squid module for caching. Both methods can effectively improve Apache's access response capabilities.

Cache in website program development, Memory Cache provided on Linux is a commonly used cache interface, which can be used in web development. For example, when developing in Java, you can call MemoryCache to cache and communicate with some data. , some large communities use such an architecture.

In addition, when using web language development, each language basically has its own cache module and method. PHP has Pear’s Cache module, and Java has even more. I am not very familiar with .net, I believe it is. there must be.

5. Mirror

Mirroring is a method often used by large websites to improve performance and data security. Mirroring technology can solve the differences in user access speeds caused by different network access providers and regions, such as the difference between ChinaNet and EduNet. Many websites build mirror sites within the education network, and the data is updated regularly or in real time. In terms of the detailed technology of mirroring, I will not go into too much detail here. There are many professional off-the-shelf solution architectures and products to choose from. There are also cheap ways to implement it through software, such as rsync and other tools on Linux.

6. Load balancing

Load balancing will be the ultimate solution for large websites to solve high-load access and a large number of concurrent requests.

Load balancing technology has been developed for many years, and there are many professional service providers and products to choose from. I have personally come across some solutions, and two of them can be used as a reference.

1) Hardware four-layer switching

The fourth layer switching uses the header information of the third and fourth layer information packets to identify the business flow according to the application interval, and The business flow of the entire interval is assigned to the appropriate application server for processing. The layer 4 switching function is like a virtual IP, pointing to the physical server. The services it transmits obey a variety of protocols, including HTTP, FTP, NFS, Telnet or other protocols. These services require complex load balancing algorithms based on physical servers. In the IP world, the service type is determined by the terminal TCP or UDP port address. In Layer 4 switching, the application range is determined by the source and terminal IP addresses, TCP and UDP ports.

In the field of hardware four-layer switching products, there are some well-known products to choose from, such as Alteon, F5, etc. These products are expensive, but they are worth the money and can provide very excellent performance and very flexible management. ability. Yahoo China used three or four Alteons to handle nearly 2,000 servers.

2) Software four-layer switching

After everyone knows the principle of hardware four-layer switch, software four-layer switching based on the OSI model came into being. , such a solution implements the same principle, but the performance is slightly worse. However, it is still easy to meet a certain amount of pressure. Some people say that the software implementation method is actually more flexible, and the processing power depends entirely on the familiarity of your configuration.

We can use the commonly used LVS on Linux to solve the four-layer software switching. LVS is Linux Virtual Server. It provides a real-time disaster response solution based on the heartbeat line, improving the system's It is robust and provides flexible virtual VIP configuration and management functions, which can meet a variety of application requirements at the same time, which is essential for distributed systems.

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