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临时启动一个http Server传送文件
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<h4 id="查看端口有没有使用："><a href="#查看端口有没有使用：" class="headerlink" title="查看端口有没有使用："></a>查看端口有没有使用：</h4><p>可以没有这一步，这里只是确认一下你预服务的端口没有被其他服务占用</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">netstat -natpl|grep 端口号</div></pre></td></tr></table></figure>
<h4 id="目标机打开个http服务："><a href="#目标机打开个http服务：" class="headerlink" title="目标机打开个http服务："></a>目标机打开个http服务：</h4><p>有些机器上会出现<code>No module named SimpleHTTPServe</code>， 重新装python吧！ 在python 3.x 中， </p>
<p>在 python 2.x 中 </p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">python -m SimpleHTTPServe port</div></pre></td></tr></table></figure>
<p>在 python 3.x 中 </p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">python -m http.server port</div></pre></td></tr></table></figure>
<h4 id="接收机下载文件："><a href="#接收机下载文件：" class="headerlink" title="接收机下载文件："></a>接收机下载文件：</h4><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">wget http://目标机ip：端口号/文件名（wget限速：wget --limit-rate=nM）</div></pre></td></tr></table></figure>
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ansible小试牛刀
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<p>1 先产生本地公钥<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">ssh-keygen -t rsa</div></pre></td></tr></table></figure></p>
<p>2 公钥拷贝到到到各个机器上</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">ssh-copy-id -i ~/.ssh/id_rsa.pub hostnam</div></pre></td></tr></table></figure>
<p>3 然后设置ansible 配置文件</p>
<p> 在/etc/ansible文件下 分别创建文件hosts 和ansible.cfg（如果没有该文件夹ansible，自行创建）</p>
<p><strong>在hosts进行相应分组</strong><br><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div></pre></td><td class="code"><pre><div class="line">[group1]</div><div class="line">hostname1</div><div class="line">hostname2</div><div class="line">[group2]</div><div class="line">hostnamex</div><div class="line">hostnamey</div></pre></td></tr></table></figure></p>
<p><strong>在ansible.cfg 文件中填写一些默认配置</strong><br><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div></pre></td><td class="code"><pre><div class="line">[defaults]</div><div class="line">host_key_checking = False</div><div class="line"></div><div class="line">sudo_user = root</div><div class="line"></div><div class="line">remote_user = 远程机器上你默认的用户名</div></pre></td></tr></table></figure></p>
<p>如果在想在远程用root 执行命令， 则可以把hosts配置成这样，<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div></pre></td><td class="code"><pre><div class="line">[group1]</div><div class="line">xxx.xxx.xxx.xxx ansible_ssh_user=test ansible_ssh_pass=xxx ansible_su_pass=xxxxx</div><div class="line">xxx.xxx.xxx.xxx ansible_ssh_user=test ansible_ssh_pass=xxx ansible_su_pass=xxxxx</div><div class="line">xxx.xxx.xxx.xxx ansible_ssh_user=test ansible_ssh_pass=xxx ansible_su_pass=xxxxxx</div></pre></td></tr></table></figure></p>
<p>4 测试是否能用</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div></pre></td><td class="code"><pre><div class="line">ansible group1 -a 'who' // 用配置文件默认的用户在远程机器上执行命令 `who`</div><div class="line">ansible group2 -a 'who' --sudo --ask-sudo-pass ／／ 用root 身份执行 `who`</div><div class="line"></div><div class="line">ansible group1 -m copy -a "src=/Users/fdafda/test.txt dest=/usr/local/" --sudo --ask-sudo-pass // 把本地文件拷贝到group1机器下的/usr/local文件下</div></pre></td></tr></table></figure>
<p>5 对于涉及过程比较多远程执行， 可以用ansible-playbook<br> <strong>编写playbook.yml 文件， 试例如下:</strong><br> <figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div></pre></td><td class="code"><pre><div class="line">- hosts: group1</div><div class="line"> become: yes</div><div class="line">become_user: root</div><div class="line">tasks:</div><div class="line"> - name: updatefile</div><div class="line"> shell: wget xxxxx/idgen/idgen_s</div><div class="line"> register: out1</div><div class="line"> - debug: msg="{{ out1.stdout }}"</div><div class="line"> -</div></pre></td></tr></table></figure></p>
<p> 执行该命令</p>
<p> <strong>然后执行如下命令</strong></p>
<pre><code><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">ansible-playbook playbook.yml</div></pre></td></tr></table></figure>
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读取文件，出现了编码错误
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<blockquote>
<p> 用scala读取本地文本文件， 出现了错误， 特此记录</p>
</blockquote>
<ul>
<li>源程序</li>
</ul>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line">import scala.io.Source</div><div class="line">Source.fromFile("logExample.txt").foreach(print)</div></pre></td></tr></table></figure>
<ul>
<li><p>错误现象</p>
<p>文本在打印过程中出现下面的错误输出 </p>
</li>
</ul>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div></pre></td><td class="code"><pre><div class="line">java.nio.charset.MalformedInputException: Input length = 1</div><div class="line">at java.nio.charset.CoderResult.throwException(CoderResult.java:277)</div><div class="line">at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:337)</div><div class="line">at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:176)</div><div class="line">at java.io.InputStreamReader.read(InputStreamReader.java:184)</div><div class="line">at java.io.BufferedReader.fill(BufferedReader.java:153)</div><div class="line">at java.io.BufferedReader.read(BufferedReader.java:174)</div><div class="line">``` </div><div class="line">- 解决方法</div><div class="line"> </div><div class="line"> 貌似好多人在平时开发中也遇到这样的错误，网上也有各种解决方法。有人尝试这样的解决方法, 貌似有人居然也解决了问题，初步猜想是，默认编码方式错误。</div></pre></td></tr></table></figure>
<p> import scala.io.Source<br> Source.fromFile(“logExample.txt”)(“UTF-8”).foreach(print)<br> <figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div></pre></td><td class="code"><pre><div class="line"></div><div class="line">通用的的解决方法</div><div class="line"></div><div class="line">**解决思路**： 检测出illegal UTF-8 byte sequence, 然后替换掉。 由于中文字符使用3个字节或者4个，所以可能被分开， 导致读取失败</div></pre></td></tr></table></figure></p>
<pre><code> import scala.io.Source
import scala.io.Codec
import java.nio.charset.CodingErrorAction
...
</code></pre><p> implicit val codec = Codec(“UTF-8”)<br> codec.onMalformedInput(CodingErrorAction.REPLACE)<br> codec.onUnmappableCharacter(CodingErrorAction.REPLACE)<br> Source.fromFile(“logExample.txt”).foreach(print)</p>
<p> ```</p>
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tiker与其他channel共用时问题
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<h4 id="ticker与其他channel共用时的问题"><a href="#ticker与其他channel共用时的问题" class="headerlink" title="ticker与其他channel共用时的问题"></a>ticker与其他channel共用时的问题</h4><p>见代码</p>
<figure class="highlight golang"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">package</span> main</div><div class="line"></div><div class="line"><span class="keyword">import</span> (</div><div class="line"> <span class="string">"fmt"</span></div><div class="line"> <span class="string">"runtime"</span></div><div class="line"> <span class="string">"time"</span></div><div class="line">)</div><div class="line"></div><div class="line"><span class="function"><span class="keyword">func</span> <span class="title">init</span><span class="params">()</span></span> {</div><div class="line"> runtime.GOMAXPROCS(runtime.NumCPU())</div><div class="line"></div><div class="line">}</div><div class="line"></div><div class="line"><span class="function"><span class="keyword">func</span> <span class="title">main</span><span class="params">()</span></span> {</div><div class="line"> ch := <span class="built_in">make</span>(<span class="keyword">chan</span> <span class="keyword">int</span>, <span class="number">1024</span>)</div><div class="line"></div><div class="line"> <span class="keyword">go</span> <span class="function"><span class="keyword">func</span><span class="params">(ch <span class="keyword">chan</span> <span class="keyword">int</span>)</span></span> {</div><div class="line"> <span class="keyword">for</span> {</div><div class="line"> val := <-ch</div><div class="line"> fmt.Printf(<span class="string">"val:%d\n"</span>, val)</div><div class="line"> }</div><div class="line"> }(ch)</div><div class="line"> tick := time.NewTicker(<span class="number">1</span> * time.Second)</div><div class="line"> <span class="keyword">for</span> i := <span class="number">0</span>; i < <span class="number">20</span>; i++ {</div><div class="line"> <span class="keyword">select</span> {</div><div class="line"> <span class="keyword">case</span> ch <- i:</div><div class="line"> <span class="keyword">case</span> <-tick.C:</div><div class="line"> fmt.Printf(<span class="string">"%d: case <-tick.C\n"</span>, i)</div><div class="line"> }</div><div class="line"> time.Sleep(<span class="number">200</span> * time.Millisecond)</div><div class="line"> }</div><div class="line"> <span class="built_in">close</span>(ch)</div><div class="line"> tick.Stop()</div><div class="line"></div><div class="line">}</div></pre></td></tr></table></figure>
<h4 id="代码结果"><a href="#代码结果" class="headerlink" title="代码结果"></a>代码结果</h4><figure class="highlight golang"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div></pre></td><td class="code"><pre><div class="line">val:<span class="number">0</span></div><div class="line">val:<span class="number">1</span></div><div class="line">val:<span class="number">2</span></div><div class="line">val:<span class="number">3</span></div><div class="line">val:<span class="number">4</span></div><div class="line">val:<span class="number">5</span></div><div class="line">val:<span class="number">6</span></div><div class="line">val:<span class="number">7</span></div><div class="line">val:<span class="number">8</span></div><div class="line">val:<span class="number">9</span></div><div class="line"><span class="number">10</span>: <span class="keyword">case</span> <-tick.C</div><div class="line">val:<span class="number">11</span></div><div class="line">val:<span class="number">12</span></div><div class="line">val:<span class="number">13</span></div><div class="line">val:<span class="number">14</span></div><div class="line">val:<span class="number">15</span></div><div class="line"><span class="number">16</span>: <span class="keyword">case</span> <-tick.C</div><div class="line">val:<span class="number">17</span></div><div class="line">val:<span class="number">18</span></div><div class="line">val:<span class="number">19</span></div></pre></td></tr></table></figure>
<p>从结果中可以看出，作者本意是要输出0～19， 却不想被打断..</p>
<h4 id="出现问题的代码"><a href="#出现问题的代码" class="headerlink" title="出现问题的代码"></a>出现问题的代码</h4><figure class="highlight golang"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">select</span> {</div><div class="line"><span class="keyword">case</span> ch <- i:</div><div class="line"><span class="keyword">case</span> <-tick.C:</div><div class="line"> fmt.Printf(<span class="string">"%d: case <-tick.C\n"</span>, i)</div><div class="line">}</div></pre></td></tr></table></figure>
<blockquote>
<p>注意： 当两个case条件都满足的时候，运行时系统会通过一个伪随机的算法决定哪个case将会被执行<br>所以当tick.C条件满足的那个循环，有某种概率造成ch<-i没有发送(虽然通道两端没有阻塞，满足发送条件)</p>
</blockquote>
<h4 id="解决方案一"><a href="#解决方案一" class="headerlink" title="解决方案一"></a>解决方案一</h4><p>一旦tick.C随机的case被随机到，就多执行一次ch<-i, 很显然，这个方法比较牵强，而且在i比较多的时候，很麻烦, 所以pass</p>
<figure class="highlight golang"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">select</span> {</div><div class="line"> <span class="keyword">case</span> ch <- i:</div><div class="line"> <span class="keyword">case</span> <-tick.C:</div><div class="line"> fmt.Printf(<span class="string">"%d: case <-tick.C\n"</span>, i)</div><div class="line"> ch <- i</div><div class="line">}</div></pre></td></tr></table></figure>
<h4 id="解决方法二"><a href="#解决方法二" class="headerlink" title="解决方法二"></a>解决方法二</h4><p>将tick.C的case单独放到一个select里面，并加入一个default（保证不阻塞）, 这种处理方法就优雅的多。（这是参考网友的思路）<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div></pre></td><td class="code"><pre><div class="line">select {</div><div class="line">case ch <- i:</div><div class="line">}</div><div class="line">select {</div><div class="line">case <-tick.C:</div><div class="line"> fmt.Printf("%d: case <-tick.C\n", i)</div><div class="line"> default:</div><div class="line">}</div></pre></td></tr></table></figure></p>
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golang超时处理
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<p> 超时对于程序操作外部资源或者管理自身程序执行时间非常重要。在 Go 语言中，因为channel与select，所以实现超时非常容易与优雅。</p>
<h4 id="案例程序一"><a href="#案例程序一" class="headerlink" title="案例程序一"></a>案例程序一</h4><figure class="highlight golang"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">package</span> main</div><div class="line"></div><div class="line"><span class="keyword">import</span> <span class="string">"time"</span></div><div class="line"></div><div class="line"><span class="keyword">import</span> <span class="string">"fmt"</span></div><div class="line"></div><div class="line"><span class="function"><span class="keyword">func</span> <span class="title">main</span><span class="params">()</span></span> {</div><div class="line"> c1 := <span class="built_in">make</span>(<span class="keyword">chan</span> <span class="keyword">string</span>)</div><div class="line"> <span class="keyword">go</span> <span class="function"><span class="keyword">func</span><span class="params">()</span></span> {</div><div class="line"> time.Sleep(time.Second * <span class="number">2</span>)</div><div class="line"> c1 <- <span class="string">"result 1"</span></div><div class="line"></div><div class="line"> }()</div><div class="line"></div><div class="line"> <span class="keyword">select</span> {</div><div class="line"></div><div class="line"> <span class="keyword">case</span> res := <-c1:</div><div class="line"></div><div class="line"> fmt.Println(res)</div><div class="line"></div><div class="line"> <span class="keyword">case</span> <-time.After(time.Second * <span class="number">1</span>):</div><div class="line"></div><div class="line"> fmt.Println(<span class="string">"timeout 1"</span>)</div><div class="line"></div><div class="line"> }</div><div class="line"></div><div class="line"> c2 := <span class="built_in">make</span>(<span class="keyword">chan</span> <span class="keyword">string</span>)</div><div class="line"></div><div class="line"> <span class="keyword">go</span> <span class="function"><span class="keyword">func</span><span class="params">()</span></span> {</div><div class="line"></div><div class="line"> time.Sleep(time.Second * <span class="number">2</span>)</div><div class="line"></div><div class="line"> c2 <- <span class="string">"result 2"</span></div><div class="line"></div><div class="line"> }()</div><div class="line"></div><div class="line"> <span class="keyword">select</span> {</div><div class="line"></div><div class="line"> <span class="keyword">case</span> res := <-c2:</div><div class="line"></div><div class="line"> fmt.Println(res)</div><div class="line"></div><div class="line"> <span class="keyword">case</span> <-time.After(time.Second * <span class="number">3</span>):</div><div class="line"></div><div class="line"> fmt.Println(<span class="string">"timeout 2"</span>)</div><div class="line"></div><div class="line"> }</div><div class="line"></div><div class="line">}</div></pre></td></tr></table></figure>
<h4 id="运行结果"><a href="#运行结果" class="headerlink" title="运行结果"></a>运行结果</h4><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line">timeout 1</div><div class="line"></div><div class="line">result 2</div></pre></td></tr></table></figure>
<h4 id="程序分析"><a href="#程序分析" class="headerlink" title="程序分析"></a>程序分析</h4><p>分析结果：主程序首先阻塞在 select中，如果在time.second <em> 1内收不到channel 发送过来的信号， 由于groutine 睡眠了time.second </em> 2了， 则select 超时，下面的程序也是按照这个逻辑运行。</p>
<h4 id="案例程序二"><a href="#案例程序二" class="headerlink" title="案例程序二"></a>案例程序二</h4><figure class="highlight golang"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line">fmt.Println(<span class="string">"hello"</span>)</div><div class="line"><-time.After(<span class="number">2</span> * time.Second)</div><div class="line">fmt.Println(<span class="string">"world"</span>)</div></pre></td></tr></table></figure>
<h4 id="程序运行结果"><a href="#程序运行结果" class="headerlink" title="程序运行结果"></a>程序运行结果</h4><p>程序首先打印出 hello, 间隔 2*time.Second 后打印出world。</p>
<h4 id="结果分析"><a href="#结果分析" class="headerlink" title="结果分析"></a>结果分析</h4><p>如果把<-time.After(2 <em> time.Second)改成 time.After(2 </em> time.Second)，则 程序会立刻打印出hello及world</p>
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golang的byte和int之间的转换
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<p>golang的byte 和int的转换</p>
<p>在使用golang做数据传输的时候，会经常遇到byte与int的互转，但golang并没有现成的方法，因此只能通过binary包来解决<br>所以，需要 ：<code>import “encoding/binary”</code>，又因为是byte的转换，所以还涉及到了bytes：<code>import “bytes”</code></p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div></pre></td><td class="code"><pre><div class="line">package main</div><div class="line"></div><div class="line">import (</div><div class="line"> "bytes"</div><div class="line"> "encoding/binary"</div><div class="line"> "fmt"</div><div class="line"> "strings"</div><div class="line">)</div><div class="line"></div><div class="line">func main() {</div><div class="line"> b := []byte{0x00, 0x00, 0x03, 0xe8}</div><div class="line"> b_buf := bytes.NewBuffer(b)</div><div class="line"> var x int32</div><div class="line"> binary.Read(b_buf, binary.BigEndian, &x)</div><div class="line"> fmt.Println(x)</div><div class="line"></div><div class="line"> fmt.Println(strings.Repeat("-", 100)) // string的一个函数</div><div class="line"></div><div class="line"> x = 1000</div><div class="line"> b_buf = bytes.NewBuffer([]byte{}) // 可以直接为空进行初始化，</div><div class="line"> binary.Write(b_buf, binary.BigEndian, x)</div><div class="line"> fmt.Println(b_buf.Bytes())</div><div class="line">}</div></pre></td></tr></table></figure>
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time_wait过多分析
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<p> 最近DBA发现Atlas和mysql之间存在大量处于time-waiter状态的connect,。 这个现象很不合理，因为Atlas是复用connect, 也就是说：当前端有一个请求过来的时候， Atlas会在当前线程的连接池中取一个可用连接，并且在处理完该请求后，会把该connect放回到连接池中，当然对于需要维持session的请求（事务、在server端处理的prepare()），只有当客户显式调用close的时候，才会把该connect放回到连接池中。因此想找找原因， 之前觉得对｀time_wait｀ 理解的还行，但具体过程也淡忘了， 之后看到了某作者写的这篇文章， 觉得写的挺详细的， 特别转载以方便以后查询。</p>
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<p>［转载文章如下］</p>
<p><strong>TIME_WAIT的产生原因</strong></p>
<p>因为TCP连接是双向的，所以在关闭连接的时候，两个方向各自都需要关闭。先发FIN包的一方执行的是主动关闭；后发FIN包的一方执行的是被动关闭。主动关闭的一方会进入TIME_WAIT状态，并且在此状态停留两倍的<br><a href="http://en.wikipedia.org/wiki/Maximum_Segment_Lifetime" target="_blank" rel="external">MSL</a>时长。</p>
<p><a href="http://www.zuoqin.me/wp-content/uploads/2015/08/3675218771011332995.png" target="_blank" rel="external"><img src="http://upload-images.jianshu.io/upload_images/1968185-2cf093f636d180b4.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240" alt="3675218771011332995"></a></p>
<p>MSL指的是报文段的最大生存时间，如果报文段在网络活动了MSL时间，还没有被接收，那么会被丢弃。关于MSL的大小，<a href="http://tools.ietf.org/search/rfc793" target="_blank" rel="external">RFC 793</a>协议中给出的建议是两分钟，不过实际上不同的操作系统可能有不同的设置，以Linux为例，通常是半分钟，两倍的MSL就是一分钟，也就是60秒，并且这个数值是硬编码在<a href="https://github.com/torvalds/linux/blob/master/include/net/tcp.h" target="_blank" rel="external">内核</a>中的，也就是说除非你重新编译内核，否则没法修改它。</p>
<p><strong>TIME_WAIT的产生原因</strong></p>
<p>因为TCP连接是双向的，所以在关闭连接的时候，两个方向各自都需要关闭。先发FIN包的一方执行的是主动关闭；后发FIN包的一方执行的是被动关闭。主动关闭的一方会进入TIME_WAIT状态，并且在此状态停留两倍的MSL时长。TIME_WAIT问题小结 – 网易杭州QA – 网易杭州 QA TeamMSL指的是报文段的最大生存时间，如果报文段在网络活动了MSL时间，还没有被接收，那么会被丢弃。关于MSL的大小，RFC 793协议中给出的建议是两分钟，不过实际上不同的操作系统可能有不同的设置，以Linux为例，通常是半分钟，两倍的MSL就是一分钟，也就是60秒，并且这个数值是硬编码在内核中的，也就是说除非你重新编译内核，否则没法修改它。TIME_WAIT状态存在的必要性。为什么主动关闭的一端不直接进入closed状态，而是要先进入time_wait并且停留两倍的MSL时长呢？这是因为TCP是建立在不可靠网络上的可靠协议。如果主动关闭的一端收到被动关闭一端的发出的FIN包后，返回ACK包，同时进入TIME_WAIT，但是由于网络的原因，主动关闭一端发送的ACK包可能会延迟，从而触发被动关闭一方重传FIN包，这样一来一回极端情况正好是2MSL。如果主动关闭的一端直接close或者不到两倍MSL时间就关闭，那么被动关闭发出重传FIN包到达，可能出现的问题是：旧的连接不存在，系统只能返回RST包；新的TCP连接已经建立，延迟包可能会干扰新连接。这都可能导致TCP不可靠。</p>
<p><strong>TIME_WAIT过多的危害</strong></p>
<p>在生产过程中，如果服务器使用短连接，那么完成一次请求后会主动断开连接，就会造成大量time_wait状态。因此我们常常在系统中会采用长连接，减少建立连接的消耗，同时也减少TIME_WAIT的产生，但实际上即使使用长连接配置不当时，当TIME_WAIT的生产速度远大于其消耗速度时，系统仍然会累计大量的TIME_WAIT状态的连接。TIME_WAIT状态连接过多就会造成一些问题。如果客户端的TIME_WAIT连接过多，同时它还在不断产生，将会导致客户端端口耗尽，新的端口分配不出来，出现错误。如果服务器端的TIME_WAIT连接过多，可能会导致客户端的请求连接失败，这在接下来举例说明。</p>
<p><strong>TIME_WAIT**</strong>问题定位**</p>
<p><strong>案例一：</strong></p>
<p>将nginx作为反向代理时，后连tomcat等服务器。测试中不同并发压力下多次、反复出现nginx服务器端口资源耗尽的问题。表现为nginx服务器出现大量time_wait状态连接，端口资源耗尽（nginx报错：cannot assign requested address ）。首先检查nginx开启了长连接keepalive，但是系统仍然出现了大量的TIME_WAIT，这就和之前提到的当系统产生TIME_WAIT的速度大于其消耗速度时，就会累计TIME_WAIT。原因是：keepalive取配置太小，将其增大后问题得以解决。(PS:nginx总的keepalive连接池大小 = keepalive取值 * nginx worker数）</p>
<p><strong>案例二：</strong></p>
<p>某应用其中一层系统架构Nginx+Tomcat，客户端发出的请求为HTTP HEAD，客户端TPS有段时间接近为0，返回Connection time out错误。<br><a href="http://www.zuoqin.me/wp-content/uploads/2015/08/6597301763611814346.png" target="_blank" rel="external"><img src="http://upload-images.jianshu.io/upload_images/1968185-a7019b821123b1c1.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240" alt="6597301763611814346"></a></p>
<p>观察大部分错误请求响应时间刚好是30s，这正好是nginx的连接超时时间配置，Tomcat没有收到这些错误请求，这意味着请求Nginx连接Tomcat都没有成功。这是为什么呢？Tomcat的连接池不够用吗？ 实际上Tomcat work线程不到200个，远小于MaxThread(1024)的值，同时还观察到Tomcat上的TIME_WAIT连接数量不正常，达到了近两万个。<br><a href="http://www.zuoqin.me/wp-content/uploads/2015/08/736338539175571363.png" target="_blank" rel="external"><img src="http://upload-images.jianshu.io/upload_images/1968185-3b6513ad036215e5.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240" alt="736338539175571363"></a><br>系统是设置了长连接的，为什么还有这么多TIME_WAIT，难道长连接没有生效吗？<br>Nginx作为反向代理，长连接配置主要有三项，upstream中的keepalive设置单个worker最大请求数，参数proxy_http_version 1.1强制转换为http1.1协议(默认支持长连接)，proxy_set_header Connection将请求头部connection为空(http1.0请求默认connection头部为close)<br>upstream backend_nosfs {<br>server 10.10.10.10:8185;<br>keepalive 1024;<br> keepalive_requests;<br>}<br>proxy_http_version 1.1;<br>proxy_set_header Connection “”;<br>Tomcat端增加配置maxKeepAliveRequests=“10000”，表示一个连接上最大请求数达到10000才会断开。<br>定位长连接问题，最简单直接的方法就是抓包，通过wireshark分析Nginx和Tomcat直接连接果然没有生效，一条连接只处理了一个请求。</p>
<p><a href="http://www.zuoqin.me/wp-content/uploads/2015/08/796011234238224070.png" target="_blank" rel="external"><img src="http://upload-images.jianshu.io/upload_images/1968185-65b6b099d0c154e3.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240" alt="796011234238224070"></a></p>
<p>为什么设置了长连接相关的配置，还是没有生效呢？经过排查发现，proxy_http_version 1.1;<br>proxy_set_header Connection “”这两项配置放在Nginx的Http域中，实际上他们要放在server域才会生效，将其位置修改后，长连接生效了，所有问题都解决了。但是我们不禁会尝试疑问TIME_WAIT出现在Tomcat而不是在Nginx上？从抓包可以看出Nginx发送给Tomcat包头部Connection为close，所以Tomcat在处理完head请求后就主动关闭，所以TIME_WAIT出现在Tomcat服务器。 配置修改后，问题解决了，TPS也上去了，之前出现的连接失败问题也没有了。<br><a href="http://www.zuoqin.me/wp-content/uploads/2015/08/3196992785579897494.png" target="_blank" rel="external"><img src="http://upload-images.jianshu.io/upload_images/1968185-61f87a3264e0372f.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240" alt="3196992785579897494"></a></p>
<p>但是为什么Tomcat服务器上的TIME_WAIT过多会导致Nginx连接失败呢？理论上说，服务器只监听在一个端口，但是会new出很多socket去处理请求，难道是socket不够用吗？再观察资源使用发现虽然TIME_WAIT连接数多，但是句柄数并不多，而socket的数量是受制于句柄数。那真正的原因是什么呢？在系统TIME_WAIT较多时，Dmesg系统出错日志为：</p>
<p><strong>nf_conntrack: table full, dropping packet</strong></p>
<p>真相大白了，Conntrack表用于记录每个连接的状态，在tcp协议中用源ip/port+目的ip/port唯一标识一个连接。记录TCP连接状态的表满了导致请求失败。查看系统ip_contrack_max配置为65536，在极端的情况下超出了其配置所有导致连接失败。<br><a href="http://www.zuoqin.me/wp-content/uploads/2015/08/1808476725466247815.png" target="_blank" rel="external"><img src="http://upload-images.jianshu.io/upload_images/1968185-8f50d819fd54826d.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240" alt="1808476725466247815"></a><br><strong>如何控制TIME_WAIT**</strong>的数量**</p>
<p>通过以上的TIME_WAIT问题，我们可以看到TIME_WAIT这个状态不存在不行，但是过多就对系统会造成困扰。那么我们应该如何控制TIME_WAIT的数量呢？</p>
<p><strong>长连接</strong></p>
<p>对于反向代理和应用服务器，最好是要配置成支持keepalive长连接，否则在系统并发增加时会导致一系列的连接问题。对于nginx+tomcat长连接的配置前面有一些介绍可以参考,其它服务器一般也是提供支持长连接配置的，设置后建议抓包测试验证。<br>一般来说长连接设置正确了TIME_WAIT数量不会暴涨，但是长连接最大请求数也是有效的，但如果应用的处理速度很快导致TIME_WAIT的产生的速度远快于TIME_WAIT的消耗速度时系统就会累计TIME_WAIT状态连接。这时候可能就要修改一些系统配置了。</p>
<p><strong>ip_conntrack</strong></p>