由于项目需要，用jmeter做了一下压测总共发送20W次的请求，设置的并发为1k。然而进行到最后发现后面的请求几乎全部failed，添加结果树后看到client报错。内容如下

java.net.NoRouteToHostException: Can't assign requested address (Address not available)
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.net.Socket.connect(Socket.java:589)
    at org.apache.http.conn.ssl.SSLConnectionSocketFactory.connectSocket(SSLConnectionSocketFactory.java:339)
    at org.apache.jmeter.protocol.http.sampler.hc.LazyLayeredConnectionSocketFactory.connectSocket(LazyLayeredConnectionSocketFactory.java:92)
    at org.apache.http.impl.conn.DefaultHttpClientConnectionOperator.connect(DefaultHttpClientConnectionOperator.java:142)
    at org.apache.jmeter.protocol.http.sampler.HTTPHC4Impl$JMeterDefaultHttpClientConnectionOperator.connect(HTTPHC4Impl.java:331)
    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.connect(PoolingHttpClientConnectionManager.java:373)
    at org.apache.http.impl.execchain.MainClientExec.establishRoute(MainClientExec.java:394)
    at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:237)
    at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:185)
    at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)
    at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
    at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
    at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
    at org.apache.jmeter.protocol.http.sampler.HTTPHC4Impl.executeRequest(HTTPHC4Impl.java:832)
    at org.apache.jmeter.protocol.http.sampler.HTTPHC4Impl.sample(HTTPHC4Impl.java:570)
    at org.apache.jmeter.protocol.http.sampler.HTTPSamplerProxy.sample(HTTPSamplerProxy.java:67)
    at org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase.sample(HTTPSamplerBase.java:1231)
    at org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase.sample(HTTPSamplerBase.java:1220)
    at org.apache.jmeter.threads.JMeterThread.doSampling(JMeterThread.java:622)
    at org.apache.jmeter.threads.JMeterThread.executeSamplePackage(JMeterThread.java:546)
    at org.apache.jmeter.threads.JMeterThread.processSampler(JMeterThread.java:486)
    at org.apache.jmeter.threads.JMeterThread.run(JMeterThread.java:253)
    at java.lang.Thread.run(Thread.java:748)

然后进行了一系列的google。大部分文章说的是port range的端口号用完导致的问题
用 netstat 命令查看了一下大部分链接都是在等待，确实端口被占用完了，然后一波操作改了范围

netstat -nt | awk '/^tcp/ {++state[$NF]} END {for(key in state) print key,"t",state[key]}'
[root@node011086 conf]# sysctl -a | grep range
net.ipv4.ip_local_port_range = 15000    65000

然后进行了一波压测发现又报错了。平均响应时间在200ms以内。百思不得其解。网上大部分操作是设置端口复用以及回收等操作，但是在执行回收操作命令的时候总是提示文件不存在。

net.ipv4.tcp_tw_reuse = 1

后来仔细看了一下官方说明发现这几个参数都是对长连接进行的优化，马上想到jmeter是否有keep alive 选项。取消勾选后果然一切正常