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设置推荐值基本原理
net.core.netdev_max_backlog30000设置包的最大数, 在输入端进行排队, 当接口接收包比内核处理更快时. 推荐设置为10GbE 链路. 对于1GbE 链路使用 8000.
net.core.wmem_max67108864对于 1GbE 链路, 设置最大数为 16MB (16777216) , 而对于10GbE链路为 64MB (67108864).
net.core.rmem_max67108864对于 1GbE 链路, 设置最大数为 16MB (16777216) , 而对于10GbE链路为 64MB (67108864).
net.ipv4.tcp_congestion_controlhtcp这看起来是 bugs 在 bic 和 cubic 上(默认) , 对于 Linux 内核上到版本 2.6.33. Redhat 5.x 内核版本是 2.6.18-x , Redhat 6.x内核版本是 2.6.32-x.
net.ipv4.tcp_congestion_window10默认情况下, Linux OS 是基于 Linux kernel 2.6.39 或以上版本.
net.ipv4.tcp_fin_timeout10This setting determines the time that must elapse before TCP/IP can release a closed connection and reuse its resources. During this TIME_WAIT state, reopening the connection to the client costs less than establishing a new connection. By reducing the value of this entry, TCP/IP can release closed connections faster, making more resources available for new connections. The default value is 60. The recommened setting lowers its to 10. You can lower this even further, but too low, and you can run into socket close errors in networks with lots of jitter.
net.ipv4.tcp_keepalive_interval30This determines the wait time between isAlive interval probes. Default value is 75. Recommended value reduces this in keeping with the reduction of the overall keepalive time.
net.ipv4.tcp_keepalive_probes5How many keepalive probes to send out before the socket is timed out. Default value is 9. Recommended value reduces this to 5 so that retry attempts will take 2.5 minutes.
net.ipv4.tcp_keepalive_time600Set the TCP Socket timeout value to 10 minutes instead of 2 hour default. With an idle socket, the system will wait tcp_keepalive_time seconds, and after that try tcp_keepalive_probes times to send a TCP KEEPALIVE in intervals of tcp_keepalive_intvl seconds. If the retry attempts fail, the socket times out.
net.ipv4.tcp_low_latency1配置 TCP 为低延时, 在吞吐量上达到低延时
net.ipv4.tcp_max_orphans16384Limit number of orphans, each orphan can eat up to 16M (max wmem) of unswappable memory
net.ipv4.tcp_max_tw_buckets1440000Maximal number of timewait sockets held by system simultaneously. If this number is exceeded time-wait socket is immediately destroyed and warning is printed. This limit exists to help prevent simple DoS attacks.
net.ipv4.tcp_no_metrics_save1禁用 连接关闭的缓存TCP metrics
net.ipv4.tcp_orphan_retries0Limit number of orphans, each orphan can eat up to 16M (max wmem) of unswappable memory
net.ipv4.tcp_rfc13371Enable a fix for RFC1337 - time-wait assassination hazards in TCP
net.ipv4.tcp_rmem10240 131072 33554432Setting is min/default/max. Recommed increasing the Linux autotuning TCP buffer limit to 32MB
net.ipv4.tcp_wmem10240 131072 33554432Setting is min/default/max. Recommed increasing the Linux autotuning TCP buffer limit to 32MB
net.ipv4.tcp_sack1启用 选择确认
net.ipv4.tcp_slow_start_after_idle0By default默认情况下, TCP starts with a single small segment, gradually increasing it by one each time. This results in unnecessary slowness that impacts the start of every request以单个小段开始, 通过每次一个逐渐增加它.这导致了不必要的拖慢, 影响了每个请求的开始.
net.ipv4.tcp_syncookies0Many default 很多默认的 Linux installations use SYN cookies to protect the system against malicious attacks that flood TCP SYN packets. The use of SYN cookies dramatically reduces network bandwidth, and can be triggered by a running Geode cluster. If your Geode cluster is otherwise protected against such attacks, disable SYN cookies to ensure that Geode network throughput is not affected. 
NOTE: if SYN floods are an issue and SYN cookies can’t be disabled, try the following安装使用 SYN 来保护系统免于 TCP SYN包洪泛攻击. 使用 SYN cookies 显著减小了网络带宽, 通过运行 Geode 集群来触发. 如果你的 Geode 集群防护受攻击, 则禁用 SYN cookies 来保障 Geode 网络吞吐量不受影响. 
注意: 如果 SYN 洪泛是一个问题, 那么 SYN cookies 则不能禁用, 尝试配置以下参数: 
net.ipv4.tcp_max_syn_backlog="16384"
net.ipv4.tcp_synack_retries="1" 
net.ipv4.tcp_max_orphans="400000"
net.ipv4.tcp_timestamps1Enable timestamps as defined in RFC1323启用时间戳(在 RFC1323中定义):
net.ipv4.tcp_tw_recycle1This enables fast recycling of TIME_WAIT sockets. The default value is 0 (disabled). Should be used with caution with load balancers.
net.ipv4.tcp_tw_reuse1This allows reusing sockets in TIME_WAIT state for new connections when it is safe from protocol viewpoint. Default value is 0 (disabled). It is generally a safer alternative to tcp_tw_recycle. The tcp_tw_reuse setting is particularly useful in environments where numerous short connections are open and left in TIME_WAIT state, such as web servers and loadbalancers.
net.ipv4.tcp_window_scaling1Turn on window scaling which can be an option to enlarge the transfer window:

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