redis 问题优化

> 本文由 [简悦 SimpRead](http://ksria.com/simpread/) 转码， 原文地址 [www.cnblogs.com](https://www.cnblogs.com/jonnyan/p/12967244.html)

maxclients  
This is a number of clients redis can handle simultaneously. The default limit is 10000.

maxclients 20000

```
但是你可能会在错误日志中看到如下警告:
# You requested maxclients of 10000 requiring at least 10032 max file descriptors.
# Redis can't set maximum open files to 10032 because of OS error: Operation not permitted.
# Current maximum open files is 4096. maxclients has been reduced to 4064 to compensate for low ulimit. If you need higher maxclients increase 'ulimit -n'.
Please try increasing open file limit first.

```

如果重新启动 Redis 后仍看到上述警告，请尝试以下操作：

打开 /lib/systemd/system/redis-server.service  
在 [Service] 下面增加一行 LimitNOFILE=64000  
然后重启 redis 服务

tcp-backlog  
如果 redis 连接很多, 建议修改此参数.  
更改此参数还需要调整 somaxconn 和 tcp_max_syn_backlog OS 参数

echo "net.core.somaxconn=65536" >> /etc/sysctl.conf  
echo "net.ipv4.tcp_max_syn_backlog=8192" >> /etc/sysctl.conf  
sysctl -p

```
WARNING: Transparent Huge Pages
For a warning like below:
# WARNING you have Transparent Huge Pages (THP) support enabled in your kernel. This will create latency and memory usage issues with Redis. To fix this issue run the command 'echo never > /sys/kernel/mm/transparent_hugepage/enabled' as root, and add it to your /etc/rc.local in order to retain the setting after a reboot. Redis must be restarted after THP is disabled.
As described in warning, please run following command.

```

echo never > /sys/kernel/mm/transparent_hugepage/enabled  
Also, add above line to the file /etc/rc.local for change to persist after a reboot. You do NOT need a reboot now.

```
WARNING: overcommit_memory
For a warning like below:
WARNING overcommit_memory is set to 0! Background save may fail under low memory condition. To fix this issue add 'vm.overcommit_memory = 1' to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit_memory=1' for this to take effect.
Run following commands:

```

echo "vm.overcommit_memory=1" >> /etc/sysctl.conf  
sysctl -p