Tuning OS Parameters

Modify some parameter settings at the operating system layer to improve server performance.

Method

Modify the parameters based on Table 1.

**Table 1** Tuning suggestions for OS parameters
Type	Parameter	Description	Suggestion
Network parameters	net.core.somaxconn	Maximum length of the socket listening queue. Increase the value if connections are frequently established.	Default value: 128; recommended value: 2048.
	net.core.netdev_max_backlog	Length of the buffer queue processed by the protocol stack. If the value is too small, packet loss may occur.	Recommended value: 10000.
	net.core.rmem_default	Default length of the receiving buffer queue.	Recommended value: 16777216.
	net.core.wmem_default	Default length of the sending buffer queue.	Recommended value: 16777216.
	net.core.rmem_max	Maximum length of the receiving buffer queue.	Recommended value: 16777216.
	net.core.wmem_max	Maximum length of the sending buffer queue.	Recommended value: 16777216.
	net.ipv4.ip_local_port_range	Local TCP/UDP port range. The local end uses a port in this range to initiate a connection with a remote end.	Recommended value: 3500 to 65535.
	net.ipv4.tcp_rmem	Size of the socket receiving buffer including the minimum value, default value, and maximum value.	Recommended minimum value, default value, and maximum value are 4096, 87380, and 16777216, respectively.
	net.ipv4.tcp_wmem	Size of the socket sending buffer including the minimum value, default value, and maximum value.	Recommended minimum value, default value, and maximum value are 4096, 65536, and 16777216, respectively.
	net.ipv4.tcp_max_syn_backlog	Number of connections in the SYN_RECVD state.	Recommended value: 16384.
	net.ipv4.tcp_fin_timeout	Duration of the FIN-WAIT-2 state after the socket is disconnected.	Recommended value: 15.
	net.ipv4.tcp_tw_reuse	Reuse the socket in the TIMEWAIT state.	Recommended value: 1.
	net.ipv4.tcp_slow_start_after_idle	Disable slow start of TCP connections from the Idle state to reduce network delay.	Recommended value: 0.
Virtual memory configuration	vm.swappiness	Use physical memory preferentially.	Recommended value: 0.
Virtual memory configuration	vm.max_map_count	Number of virtual memory areas that a process can have.	Recommended value: 655360.
AIO configuration	fs.aio-max-nr	Number of asynchronous I/O requests.	Recommended value: 1048576.

Viewing and Modifying OS Parameters

Modify the OS kernel parameters because these parameters are important to the system performance and stability. You are advised to operate under the guidance of an experienced system administrator.

View and modify the system parameters in Table 1 in either of the following ways:

The following commands are used to temporarily change parameter values. The parameters will be restored to default after the OS is restarted.
For example, run the following command to view the value of net.core.somaxconn:
```
sysctl net.core.somaxconn
```
Run the following command to change the value of net.core.somaxconn:
```
sysctl -w net.core.somaxconn=NEW_VALUE
```
To permanently change parameter values, for example, the value of net.core.somaxconn, modify the /etc/sysctl.conf configuration file and make the modification take effect:
1. Open the /etc/sysctl.conf file.
```
vi /etc/sysctl.conf
```
2. Press i to enter the insert mode and add the following content to the /etc/sysctl.conf file:
```
net.core.somaxconn=NEW_VALUE
```
3. Press Esc, type :wq!, and press Enter to save the file and exit.
4. Run the command for the modification to take effect:
```
sysctl -p
```

Parent topic: OS Tuning