net.core.somaxconn
Linux 操作系统全局参数，每个 TCP 监听端口的队列长度。在 CentOS/RHEL 7.9 中，默认值为128，对于高并发场景都建议调大该值。
1.官方描述
The Linux Kernel somaxconn - INTEGER
Limit of socket listen() backlog, known in userspace as SOMAXCONN. Defaults to 4096. (Was 128 before linux-5.4) See also tcp_max_syn_backlog for additional tuning for TCP sockets.
取值范围：
- In RHEL 6 & RHEL 7, the sk_max_ack_backlog field of the sock
structure is defined as unsigned short which limits the values to 16
bits whose maximum value is 65535. - In RHEL 8, sk_max_ack_backlog
field of the sock structure is defined as u32 which limits the values
to 32 bits whose maximum value is 2147483647.
2.不同应用的配置建议
2.1.Oracle WebLogic Server
- Number of clients: Set somaxconn should be set to at least 1024 to
allow for a large number of client server connections. - Number of queued packets: Set netdev_max_backlog to at least 32768 to minimize packet loss.
2.2.ZooKeeper
On linux, below parameter :
net.core.somaxconn
needs to be larger than above “clientPortBacklog” to correctly configure listen socket backlog
2.3.TiDB
检查各项内核参数的值：
…
net.core.somaxconn: 32768
2.4.Nginx
Increase the value of the net.core.somaxconn kernel parameter from its default value (128) to a value high enough for a large burst of traffic. In this example, it’s increased to 4096.
3.配置方法
3.1.临时生效
sysctl -w net.core.somaxconn=10240
3.2.永久生效
echo "net.core.somaxconn = 10240" >>/etc/sysctl.conf
sysctl -p