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itemtype="http://schema.org/Person"><meta itemprop="name" content="虾丸派"><meta itemprop="description" content="记录知识 | 分享技术"><meta itemprop="image" content="/images/favicon-1536x1536-playpi.png"></span><span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization"><meta itemprop="name" content="虾丸派"></span><header class="post-header"><h2 class="post-title" itemprop="name headline">Elasticsearch 异常之 too many open files</h2><div class="post-meta"><span class="post-time"><span class="post-meta-item-text">发表于</span> <time title="创建于" itemprop="dateCreated datePublished" datetime="2018-07-09T21:15:08+08:00">2018-07-09 </time></span><span class="post-category"><span class="post-meta-divider">|</span> <span class="post-meta-item-text">分类于</span> <span itemprop="about" itemscope itemtype="http://schema.org/Thing"><a href="/categories/big-data-technical-knowledge/" itemprop="url" rel="index"><span itemprop="name">大数据技术知识</span> </a></span></span><span id="busuanzi_container_page_pv" style="display:none"><span class="post-meta-divider">|</span> 阅读次数 <span id="busuanzi_value_page_pv"></span></span><div class="post-wordcount"><span class="post-meta-item-text">字数统计</span> <span title="字数统计">2,376字 </span><span class="post-meta-divider">|</span> <span class="post-meta-item-text">阅读时长 ≈</span> <span title="阅读时长">10分钟</span></div></div></header><div class="post-body" itemprop="articleBody"><p>目前在 <code>Java</code> 项目中普遍使用 <code>Elasticsearch</code> 的 <code>Java API</code> 进行连接集群、发送请求、解析结果，方便快捷。在某一次运行时发生了异常，异常信息如下：</p><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line">java.net.SocketException: Too many open files</span><br><span class="line"> at java.net.Socket.createImpl (Socket.java:460)</span><br><span class="line"> at java.net.Socket.connect (Socket.java 587)</span><br><span class="line"> at sun.net.NetworkClient.doConnect (NetworkClient.java 175)</span><br><span class="line"> at sun.net.www.http.HttpClient.openServer (HttpClient.java 463)</span><br><span class="line"> at sun.net.www.http.HttpClient.openServer (HttpClient.java 558)</span><br><span class="line"> at sun.net.www.http.HttpClient.<init>(HttpClient.java 242)</span><br><span class="line"> at sun.net.www.http.HttpClient.New (HttpClient.java 339)</span><br><span class="line"> at sun.net.www.http.HttpClient.New (HttpClient.java 357)</span><br><span class="line"> at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient (HttpURLConnection.java 1220)</span><br><span class="line"> sun.net.www.protocol.http.HttpURLConnection.plainConnect0 (HttpURLConnection.java 1156)</span><br><span class="line"> sun.net.www.protocol.http.HttpURLConnection.plainConnect (HttpURLConnection.java 1050)</span><br><span class="line"> sun.net.www.protocol.http.HttpURLConnection.connect (HttpURLConnection.java 984)</span><br><span class="line"> sun.net.www.protocol.http.HttpURLConnection.getOutputStream0 (HttpURLConnection.java 1334)</span><br><span class="line"> sun.net.www.protocol.http.HttpURLConnection.getOutputStream (HttpURLConnection.java 1309)</span><br><span class="line"> ...(省略更多业务代码)</span><br><span class="line"> </span><br><span class="line"> 备注：以上异常信息实际是因为创建 HTTP 链接过多，超过了操作系统设置的最大值，这个异常与创建 TransportClient 过多类似，所以拿它举例，实际排查思路还是以 TransportClient 为准。</span><br></pre></td></tr></table></figure><p>查看异常信息里面的重点内容：<code>java.net.SocketException: Too many open files</code>，有时候在中文运行系统环境中会显示：<code>打开的文件过多</code>，其实是一个意思。</p><p>本文介绍遇到此问题后分析、解决的方法，开发环境基于 <code>Elasticsearch v1.7.5</code>【这是一个很古老的版本了】、<code>JDK v1.8</code>，其它版本的报错详细信息可能会大同小异，但是主要异常信息以及原因是一致的。</p><a id="more"></a><h1 id="问题出现"><a href="# 问题出现" class="headerlink" title="问题出现"></a>问题出现</h1><p>首先说明一下业务代码中的相关逻辑，使用 <code>Elasticsearch</code> 中的 <code>TransportClient</code> 接口连接集群，进行查询操作，<code>TransportClient</code> 接口的使用方式可以参考我的另外一篇博文：<a href="https://blog.playpi.org/2018022401.html" target="_blank" rel="noopener">Elasticsearch 根据查询条件删除数据的 API</a> 。</p><p>今天启动程序正常运行一段时间后，抛出异常，持续多次，日志内容如下：</p><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line">java.net.SocketException: Too many open files</span><br><span class="line"> at java.net.Socket.createImpl (Socket.java:460)</span><br><span class="line"> at java.net.Socket.connect (Socket.java 587)</span><br><span class="line"> at sun.net.NetworkClient.doConnect (NetworkClient.java 175)</span><br><span class="line"> at sun.net.www.http.HttpClient.openServer (HttpClient.java 463)</span><br><span class="line"> at sun.net.www.http.HttpClient.openServer (HttpClient.java 558)</span><br><span class="line"> at sun.net.www.http.HttpClient.<init>(HttpClient.java 242)</span><br><span class="line"> at sun.net.www.http.HttpClient.New (HttpClient.java 339)</span><br><span class="line"> at sun.net.www.http.HttpClient.New (HttpClient.java 357)</span><br><span class="line"> at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient (HttpURLConnection.java 1220)</span><br><span class="line"> sun.net.www.protocol.http.HttpURLConnection.plainConnect0 (HttpURLConnection.java 1156)</span><br><span class="line"> sun.net.www.protocol.http.HttpURLConnection.plainConnect (HttpURLConnection.java 1050)</span><br><span class="line"> sun.net.www.protocol.http.HttpURLConnection.connect (HttpURLConnection.java 984)</span><br><span class="line"> sun.net.www.protocol.http.HttpURLConnection.getOutputStream0 (HttpURLConnection.java 1334)</span><br><span class="line"> sun.net.www.protocol.http.HttpURLConnection.getOutputStream (HttpURLConnection.java 1309)</span><br><span class="line"> ...(省略更多业务代码)</span><br><span class="line"> </span><br><span class="line"> 备注：以上异常信息实际是因为创建 HTTP 链接过多，超过了操作系统设置的最大值，这个异常与创建 TransportClient 过多类似，所以拿它举例，实际排查思路还是以 TransportClient 为准。</span><br></pre></td></tr></table></figure><p><strong>备注 </strong>：以上异常信息实际是因为创建 <code>HTTP</code> 链接过多，超过了操作系统设置的最大值，这个异常与创建 <code>TransportClient</code> 过多类似，所以拿它举例，实际排查思路还是以 <code>TransportClient</code> 为准。</p><p><img src="https://raw.githubusercontent.com/iplaypi/img-playpi/master/img/2018/20191117154740.png" alt="异常日志" title="异常日志"></p><p>在这里看不到具体的代码出错位置，首先需要跟踪找到业务代码。经过排查，发现是在一个关于 <code>Elasticsearch</code> 的工具类中，在创建 <code>TransportClient</code> 连接实例的时候，抛出这个异常。</p><p>代码已经被我上传至 <code>GitHub</code>，详见：<a href="https://github.com/iplaypi/iplaypistudy/tree/master/iplaypistudy-elasticsearch/src/main/java/org/playpi/study/util" target="_blank" rel="noopener">EsClusterUtil.initTransportClient</a> ，搜索类名 <code>EsClusterUtil</code> 即可，仅供参考【此代码的书写基于 <code>Elasticsearch v5.6.8</code>，与 <code>v.1.7.5</code> 略有不同】。</p><p>方法代码如下：</p><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br></pre></td><td class="code"><pre><span class="line">/**</span><br><span class="line"> * 根据主机端口列表 / 集群名称，创建 es 连接 </span><br><span class="line"> * 由于开启连接需要占用资源，不要开启过多，并在使用完毕后及时关闭 </span><br><span class="line"> *</span><br><span class="line"> * @param hostArr</span><br><span class="line"> * @param clusterName</span><br><span class="line"> * @return</span><br><span class="line"> */</span><br><span class="line">public static TransportClient initTransportClient (String [] hostArr, String clusterName) {</span><br><span class="line"> TransportClient client = null;</span><br><span class="line"> Settings settings = Settings.builder ()</span><br><span class="line"> .put ("cluster.name", clusterName)</span><br><span class="line"> .put ("client.transport.ping_timeout", "60s")</span><br><span class="line"> .put ("client.transport.sniff", true)// 开启嗅探特性 </span><br><span class="line"> .build ();</span><br><span class="line"> /**</span><br><span class="line"> * String [] hostArr = new String []{"hostname1:port", "hostname2:port", "hostname3:port"};</span><br><span class="line"> */</span><br><span class="line"> TransportAddress [] transportAddresses = new InetSocketTransportAddress [hostArr.length];</span><br><span class="line"> for (int i = 0; i < hostArr.length; i++) {</span><br><span class="line"> String [] parts = hostArr [i].split (":");</span><br><span class="line"> try {</span><br><span class="line"> InetAddress inetAddress = InetAddress.getByName (parts [0]);</span><br><span class="line"> transportAddresses [i] = new InetSocketTransportAddress (inetAddress, Integer.parseint (parts [1]));</span><br><span class="line"> }</span><br><span class="line"> catch (UnknownHostException e) {</span><br><span class="line"> log.error ("!!!!es 连接初始化出错: " + e.getMessage (), e);</span><br><span class="line"> return client;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> client = new PreBuiltTransportClient (settings)</span><br><span class="line"> .addTransportAddresses (transportAddresses);</span><br><span class="line"> return client;</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p>可以看到，这里的方法不是单例模式，仅仅是创建一个 <code>TransportClient</code> 实例。</p><p>如果在业务代码中频繁调用这个方法，可能会创建大量的连接，而如果又没有及时关闭，有潜在的危险。</p><p>顺着这个思路继续找下去，的确，在业务代码中会创建大量的连接，然后请求 <code>Elasticsearch</code> 集群，更为奇葩的是，在使用完成后也没有关闭 <code>TransportClient</code> 连接，而是不管不问，让它自生自灭。</p><p>这样怎么能行，肯定会有大量连接没有关闭，占用着 <code>Elasticsearch</code> 集群的资源。</p><h1 id="问题分析解决"><a href="# 问题分析解决" class="headerlink" title="问题分析解决"></a>问题分析解决</h1><p>上面对于问题的分析、排查基本完成，下面就要仔细分析集群的设置以及给出可行的解决思路。</p><p>先使用 <code>Elasticsearch</code> 官方的 <code>api</code> 查看集群的文件句柄使用情况：<code>GET /_nodes/stats?pretty</code>，找到 <code>process</code> 下面的配置 <code>open_file_descriptors</code>、<code>max_file_descriptors</code> 。</p><p><code>v5.6.8</code> 的查看结果</p><p><img src="https://raw.githubusercontent.com/iplaypi/img-playpi/master/img/2018/20191117184201.png" alt="v5.6.8 查看 open_file_descriptors" title="v5.6.8 查看 open_file_descriptors"></p><p><code>v1.7.5</code> 的查看结果，没有 <code>max_file_descriptors</code> 显示</p><p><img src="https://raw.githubusercontent.com/iplaypi/img-playpi/master/img/2018/20191117184244.png" alt="v1.7.5 查看 open_file_descriptors" title="v1.7.5 查看 open_file_descriptors"></p><p>使用 <code>GET _nodes/stats/process?filter_path=**.max_file_descriptors</code> 查看集群的最大限制，和上面的结果一致，可以看到是数十万，已经是很大的数值了【<code>v5.6.8</code> 可以查看，<code>v1.7.5</code> 不可查看】。</p><p><img src="https://raw.githubusercontent.com/iplaypi/img-playpi/master/img/2018/20191117184253.png" alt="v5.6.8 查看 max_file_descriptors" title="v5.6.8 查看 max_file_descriptors"></p><p>根据 <code>open_file_descriptors</code> 的结果，仅仅使用了数千个，而集群允许使用数十万个【<code>max_file_descriptors</code> 参数】，所以业务中不可能使用这么多连接，真的使用这么多集群恐怕无法正常运行了。</p><p>由此进一步猜测，业务中的报错可能和执行进程的操作系统、用户有关，根据官网的介绍：<a href="https://www.elastic.co/guide/en/elasticsearch/reference/5.6/file-descriptors.html" target="_blank" rel="noopener">file-descriptors</a> ，不妨查看系统的配置，打开系统的 <code>cat /etc/security/limits.conf</code> 文件，可以看到限制的最大文件句柄数为 65535【星号表示针对所有的用户生效】。</p><p><img src="https://raw.githubusercontent.com/iplaypi/img-playpi/master/img/2018/20191117184050.png" alt="查看系统的 limits" title="查看系统的 limits"></p><p>还可以继续使用 <code>ulimit -a</code> 验证操作系统对当前用户的限制是不是这么大，如下图所示，根据 <code>open files</code> 配置，的确是的。</p><p><img src="https://raw.githubusercontent.com/iplaypi/img-playpi/master/img/2018/20191117184018.png" alt="查看用户的 ulimit" title="查看用户的 ulimit"></p><p>这么一来，程序运行时如果创建的连接数超过 65535 个，就会被操作系统限制，而这个数万级别的数量还是有可能的。</p><p>至此，问题基本分析出来了，主要就是业务代码中创建的 <code>Elasticsearch</code> 连接数过多，被操作系统拒绝了，才会导致本文开头的异常。那么解决方案就很简单了，在业务代码中限制创建的连接数即可【使用单例模式创建连接或者使用完成后及时关闭连接】。</p><p>最后总结一下：</p><p>这种创建连接的操作，最好使用单例模式进行设计，这样无论业务代码怎么调用，都不会创建过多的实例，从根本上杜绝滥用的情况。</p><p>在使用这种占用资源的场景下，例如：<code>Elasticsearch</code> 的 <code>TransportClient</code> 对象，使用完成后要及时关闭，不能占用着连接不使用但是又不关闭，这样肯定是给 <code>Elasticsearch</code> 集群造成压力，其它文件流也是类似。等到连接数达到最大时，<code>Elasticsearch</code> 集群也就会一直报错：打开的文件过多。</p><p>但是，还要注意一点，在不使用单例模式的情况下，合理地关闭连接也可能会有问题，因为 <code>Elasticsearch</code> 会维护一个连接池，代码显示 <code>close</code> 后连接并不一定真的被关闭，因此使用单例模式是最好的选择。</p><p>加大系统的文件句柄数【或者是用户的文件句柄数】不是根本解决办法，只是滋养了烂代码的生存空间，最终还是会重现问题。最好的方式当然是把生成 <code>TransportClient</code> 的方法改成单例模式，或者使用完成后及时关闭连接，简单正确，可以永久解决此问题。</p><h1 id="备注"><a href="# 备注" class="headerlink" title="备注"></a>备注</h1><p>以上排查思路以客户端连接数为切入点，因为一开始查到 <code>Elasticsearch</code> 集群的 <code>max_file_descriptors</code> 参数设置的足够大，所以不太可能是 <code>Elasticsearch</code> 集群的问题，转而把关注点放到客户端的使用上。其实，无论是使用 <code>HTTP</code> 连接还是官方的 <code>TransportClient</code> 连接，如果连接数超过了操作系统的设置，就会出现 <code>Too many open files</code> 这个异常。</p><p>关于文件描述符的官网介绍：<a href="https://www.elastic.co/guide/en/elasticsearch/reference/5.6/file-descriptors.html" target="_blank" rel="noopener">file-descriptors</a> 。</p><p>使用单例模式，解决问题，<a href="https://www.cnblogs.com/GoQC/p/6803341.html" target="_blank" rel="noopener">博客园 </a>。</p><p>关于用户、系统的文件句柄数上限，<a href="https://elasticsearch.cn/question/4702" target="_blank" rel="noopener">elastic 中文社区 </a>。如果是启动 <code>Elasticsearch</code> 进程时出现这个问题，导致启动失败，可以查看对应的进程占用了多少个文件句柄，使用命令：<code>losf -p pid |wc -l</code>。如果是 <code>Elasticsearch</code> 本身占用了过多的文件句柄，可以考虑是不是索引的段个数设置不合理，参考：<a href="https://www.jianshu.com/p/0ceb59025521" target="_blank" rel="noopener"> 索引段个数的问题 </a>，可以使用 <code>GET your_index_name/_segments</code> 查看段信息。</p><p>关于系统配置生效问题：<a href="http://imsilence.github.io/2015/09/16/elasticsearch/elasticsearch_max_open_files" target="_blank" rel="noopener">记一次修改 elasticsearch 文件描述符数量</a> 。</p></div><div><div id="wechat_subscriber" style="display:block;padding:10px 0;margin:20px auto;width:100%;text-align:center"><img id="wechat_subscriber_qcode" src="/images/wechat-qr-personal.jpg" alt="虾丸派 wechat" 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