一.内核参数修改

参数说明

#最大的TCP数据接收窗口（字节）

#当前值：

net.core.rmem_max=16777216

#最大的TCP数据发送窗口（字节）。

#当前值

net.core.wmem_max=16777216

#为自动调优定义socket使用的内存。第一个值是为socket接收缓冲区分配的最少字节数；第二个值是默认值（该值会被rmem_default覆盖），缓冲区在系统负载不重的情况下可以增长到这个值；第三个值是接收缓冲区空间的最大字节数（该值会被rmem_max覆盖）。

#当前值

net.ipv4.tcp_rmem="4096 87380 16777216"

#为自动调优定义socket使用的内存。第一个值是为socket发送缓冲区分配的最少字节数；第二个值是默认值（该值会被wmem_default覆盖），缓冲区在系统负载不重的情况下可以增长到这个值；第三个值是发送缓冲区空间的最大字节数（该值会被wmem_max覆盖）。

#当前值

net.ipv4.tcp_wmem="4096 16384 16777216"

调整queue Sizes

#net.core.somaxconn controls the size of the connection listening queue

#当前值:128

net.core.somaxconn=4096

#在每个网络接口接收数据包的速率比内核处理这些包的速率快时，允许送到队列的数据包的最大数目

#当前值：

net.core.netdev_max_backlog=16384

#已修改

#net.ipv4.tcp_max_syn_backlog=8192

#已修改

#net.ipv4.tcp_syncookies=1

 

修改办法：

1.使用root用户，vi /etc/sysctl.conf ，新增如下内容：

net.core.rmem_max=16777216

net.core.wmem_max=16777216

net.ipv4.tcp_rmem="4096 87380 16777216"

net.ipv4.tcp_wmem="4096 16384 16777216"

net.core.somaxconn=4096

net.core.netdev_max_backlog=16384

 

2.执行命令：sysctl -p

 

回退方法：

1.先回退/etc/sysctl.conf添加的内容

2.使用sysctl -w执行该参数对应的值

sysctl -w net.core.rmem_max=修改前的值

sysctl -w net.core.wmem_max=修改前的值

sysctl -w net.ipv4.tcp_rmem=修改前的值

sysctl -w net.ipv4.tcp_wmem=修改前的值

sysctl -w net.core.somaxconn=128

sysctl -w net.core.netdev_max_backlog=1000

说明：修改前的值可查看其他未调整的服务器值，通过sysctl -a|grep rmem_max

 

open files数量修改

说明

inux系统默认open files数目为1024, 有时应用程序会报Too many open files的错误，是因为open files 数目不够。这就需要修改ulimit和file-max。特别是提供大量静态文件访问的web服务器，缓存服务器（如squid）, 更要注意这个问题。

当前值：

soft nofile 8192

hard nofile 8192

修改后：

soft nofile 20480

hard nofile 20480

 

修改办法：

使用root用户,vi /etc/security/limits.conf

修改：

soft nofile 20480

hard nofile 20480

 

jetty高可用常见参数设置

Operating System Tuning

Both the server machine and any load generating machines need to be tuned to support many TCP/IP connections and high throughput.

Linux

Linux does a reasonable job of self-configuring TCP/IP, but there are a few limits and defaults that you should increase. You can configure most of these in /etc/security/limits.conf or via sysctl.

TCP Buffer Sizes

You should increase TCP buffer sizes to at least 16MB for 10G paths and tune the auto-tuning (keep in mind that you need to consider buffer bloat).

$ sysctl -w net.core.rmem_max=16777216
$ sysctl -w net.core.wmem_max=16777216
$ sysctl -w net.ipv4.tcp_rmem="4096 87380 16777216"
$ sysctl -w net.ipv4.tcp_wmem="4096 16384 16777216"

Queue Sizes

net.core.somaxconn controls the size of the connection listening queue. The default value is 128. If you are running a high-volume server and connections are getting refused at a TCP level, you need to increase this value. This setting can take a bit of finesse to get correct: if you set it too high, resource problems occur as it tries to notify a server of a large number of connections, and many remain pending, but if you set it too low, refused connections occur.

 $ sysctl -w net.core.somaxconn=4096

The net.core.netdev_max_backlog controls the size of the incoming packet queue for upper-layer (Java) processing. The default (2048) may be increased and other related parameters adjusted with:

$ sysctl -w net.core.netdev_max_backlog=16384
$ sysctl -w net.ipv4.tcp_max_syn_backlog=8192
$ sysctl -w net.ipv4.tcp_syncookies=1

Ports

If many outgoing connections are made (for example, on load generators), the operating system might run low on ports. Thus it is best to increase the port range, and allow reuse of sockets in TIME_WAIT:

$ sysctl -w net.ipv4.ip_local_port_range="1024 65535"
$ sysctl -w net.ipv4.tcp_tw_recycle=1

File Descriptors

Busy servers and load generators may run out of file descriptors as the system defaults are normally low. These can be increased for a specific user in /etc/security/limits.conf:

theusername            hard nofile     40000
theusername            soft nofile     40000

Congestion Control

Linux supports pluggable congestion control algorithms. To get a list of congestion control algorithms that are available in your kernel run:

$ sysctl net.ipv4.tcp_available_congestion_control

If cubic and/or htcp are not listed, you need to research the control algorithms for your kernel. You can try setting the control to cubic with:

$ sysctl -w net.ipv4.tcp_congestion_control=cubic

参考：https://www.eclipse.org/jetty/documentation/current/high-load.html