The use of swap [6] was an essential part of using smaller UNIX machines in the early 1990s. It is still useful (like having a spare tire in your vehicle) when nasty memory leaks interfere with your work. The machine will slow down but in most cases will still be usable to finish its assigned task. Free software developers have been making great strides to reduce and eliminate program errors so before changing kernel parameters consider updating to a newer version of your application and related libraries first.
If you run numerous tasks, then the inactive tasks will be swapped out to disk, making better use of memory with your active tasks. Video editing and other large memory consuming applications often have recommended amounts of memory and disk space. If you have an older machine which cannot have a memory upgrade, then making more swap available might be a good temporary solution for you (see [6] on how to learn more about that).
The swapping can happen on a separate partition or on a swap file. The partition is faster and favored by many database applications. The file approach is more flexible (see the dphys-swapfile package in Debian GNU/Linux [7]). Having more than one physical device for swapping allows the Linux kernel to choose the device that is most rapidly available (lower latency).
vm.swappiness
The default value of vm.swappiness is 60 and represents the percentage of the free memory before activating swap. The lower the value, the less swapping is used and the more memory pages are kept in physical memory.
The value of 60 is a compromise that works well for modern desktop systems. A smaller value is a recommended option for a server system, instead. As the Red Hat Performance Tuning manual points out [8], a smaller swappiness value is recommended for database workloads. For example, for Oracle databases, Red Hat recommends a swappiness value of 10. In contrast, for MariaDB databases, it is recommended to set swappiness to a value of 1 [9].
Changing the value directly influences the performance of the Linux system. These values are defined:
* 0: swap is disable
* 1: minimum amount of swapping without disabling it entirely
* 10: recommended value to improve performance when sufficient memory exists in a system
* 100: aggressive swapping
As shown above the cat command helps to read the value. Also, the sysctl command gives you the same result:
# sysctl vm.swappiness
vm.swappiness = 60
#
Keep in mind that the sysctl command is only available to an administrative user. To set the value temporarily set the value in the /proc file system as follows:
# echo 10 > /proc/sys/vm/swappiness
As an alternative you may use the sysctl command as follows:
# sysctl -w vm.swappiness=10
To set the value permanently, open the file /etc/sysctl.conf as an administrative user and add the following line:
Using Swap
The use of swap [6] was an essential part of using smaller UNIX machines in the early 1990s. It is still useful (like having a spare tire in your vehicle) when nasty memory leaks interfere with your work. The machine will slow down but in most cases will still be usable to finish its assigned task. Free software developers have been making great strides to reduce and eliminate program errors so before changing kernel parameters consider updating to a newer version of your application and related libraries first.
If you run numerous tasks, then the inactive tasks will be swapped out to disk, making better use of memory with your active tasks. Video editing and other large memory consuming applications often have recommended amounts of memory and disk space. If you have an older machine which cannot have a memory upgrade, then making more swap available might be a good temporary solution for you (see [6] on how to learn more about that).
The swapping can happen on a separate partition or on a swap file. The partition is faster and favored by many database applications. The file approach is more flexible (see the dphys-swapfile package in Debian GNU/Linux [7]). Having more than one physical device for swapping allows the Linux kernel to choose the device that is most rapidly available (lower latency).
vm.swappiness
The default value of vm.swappiness is 60 and represents the percentage of the free memory before activating swap. The lower the value, the less swapping is used and the more memory pages are kept in physical memory.
The value of 60 is a compromise that works well for modern desktop systems. A smaller value is a recommended option for a server system, instead. As the Red Hat Performance Tuning manual points out [8], a smaller swappiness value is recommended for database workloads. For example, for Oracle databases, Red Hat recommends a swappiness value of 10. In contrast, for MariaDB databases, it is recommended to set swappiness to a value of 1 [9].
Changing the value directly influences the performance of the Linux system. These values are defined:
* 0: swap is disable
* 1: minimum amount of swapping without disabling it entirely
* 10: recommended value to improve performance when sufficient memory exists in a system
* 100: aggressive swapping
As shown above the cat command helps to read the value. Also, the sysctl command gives you the same result:
# sysctl vm.swappiness
vm.swappiness = 60
#
Keep in mind that the sysctl command is only available to an administrative user. To set the value temporarily set the value in the /proc file system as follows:
# echo 10 > /proc/sys/vm/swappiness
As an alternative you may use the sysctl command as follows:
# sysctl -w vm.swappiness=10
To set the value permanently, open the file /etc/sysctl.conf as an administrative user and add the following line:
vm.swappiness = 10