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This article will explain in detail the Linux kernel parameters that need to be adjusted in Java large-scale middleware systems, and the content of the article is of high quality, so the editor will share it for you as a reference. I hope you will have some understanding of the relevant knowledge after reading this article.

As a Java developer, it is inevitable to develop or use some middleware. For Java development middleware, in addition to JVM parameters must be adjusted, some kernel parameters of Linux must also be adjusted.

It all has something to do with the disk file IO, network communication, memory management, and the number of threads, because our middleware system only deals with these when it is running.

Vm.overcommit_memory

This parameter has three values to choose from, 0, 1, and 2.

If the value is 0, when your middleware system applies for memory, the operating system kernel will check whether the available memory is enough, and if it is enough, it will allocate memory to you, and if you feel that the remaining memory is not enough, simply reject your application, resulting in your application for memory failure, which leads to an abnormal error in the middleware system. Therefore, it is generally necessary to adjust the value of this parameter to 1, which means that all available physical memory is allowed to be allocated to you, as long as there is memory for you to use, so as to avoid the problem of failed applications for memory.

For example, the Redis deployed in our online environment was rejected when you need to apply for large memory when you snapshot save data to a disk file because this parameter is 0, resulting in an abnormal error.

You can modify it with the following command:

Echo 'vm.overcommit_memory=1' > > / etc/sysctl.conf

Vm.max_map_count

It is also important that the value of this parameter affects the number of threads that can be opened by the middleware system.

If this parameter is too small, it may sometimes cause some middleware to fail to open enough threads, resulting in an error or even a failure of the middleware system.

His default value is 65536, but sometimes this value is not enough. For example, the Kafka cluster deployed in the production environment of big data team once reported this exception, saying that not enough threads could be opened, which directly led to Kafka downtime.

You can modify it with the following command:

Echo 'vm.max_map_count=655360' > > / etc/sysctl.conf

Vm.swappiness

This parameter is used to control the swap behavior of the process, which simply means that the operating system will use part of the disk space as the swap area, and then if some processes may not be too active now, the operating system will adjust the process to sleep, put the data in the process into the swap area on the disk, and then let the process free up the memory space it used to occupy. Give it to other active processes to use.

If the value of this parameter is set to 0, it means that try not to put any process in the disk swap area, and try to use physical memory.

If the value of this parameter is 100, it means to put as many processes as possible into the swap area of the disk, freeing up memory for active processes to use.

The default value of this parameter is 60, which is a bit high, which may cause our middleware to be forced to free up memory space and put it in the disk swap area when the middleware is not active. Therefore, it is usually recommended to adjust this parameter smaller in the production environment, such as setting it to 10, try to use physical memory, do not put the disk swap area.

You can modify it with the following command:

Echo 'vm.swappiness=10' > > / etc/sysctl.conf

Ulimit

This is used to control the maximum number of file connections on the linux. The default value may be 1024, which is generally not enough, because when you read and write disk files frequently, or when you are communicating on the network, it will have something to do with this parameter.

For a middleware system, it is certainly worthwhile not to use default values. If you use default values, the following errors are likely to occur online:

Error: too many open files

Therefore, it is generally recommended to modify this value with the following command:

Echo 'ulimit-n 1000000' > > / etc/profile

A little summary.

Middleware systems definitely have to open a large number of threads (related to vm.max_map_count).

And there is a lot of network communication and disk IO (related to ulimit).

Then use a lot of memory (related to vm.swappiness and vm.overcommit_memory).

So the adjustment of OS kernel parameters often revolves around what is most relevant to the running of the middleware system.

This is the end of the Linux kernel parameters that need to be adjusted in the Java large middleware system. I hope the above content can be helpful to everyone and learn more knowledge. If you think the article is good, you can share it for more people to see.

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