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    <article id="post-loadBalance" class="article article-type-post" itemscope itemprop="blogPost">
  
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      <a href="/2018/12/23/loadBalance/" class="article-date">
  	<time datetime="2018-12-23T13:28:01.000Z" itemprop="datePublished">2018-12-23</time>
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      <a class="article-title" href="/2018/12/23/loadBalance/">负载均衡常用软件及算法</a>
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    <div class="toc-title">目录</div>
    <ol class="toc"><li class="toc-item toc-level-2"><a class="toc-link" href="#负载均衡组件"><span class="toc-text">负载均衡组件</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#负载均衡策略"><span class="toc-text">负载均衡策略</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#服务可用性探测"><span class="toc-text">服务可用性探测</span></a></li></ol>
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        <h2 id="负载均衡组件"><a href="#负载均衡组件" class="headerlink" title="负载均衡组件"></a>负载均衡组件</h2><ul>
<li>硬件负载均衡-F5，流量百万级</li>
<li>传输层负载均衡-LVS，十万级</li>
<li>应用层负责均衡-nignx,万级 </li>
<li>NAT技术其实也是一种负载均衡</li>
</ul>
<p><img src="img/lb.png" alt="load_balance"></p>
<h2 id="负载均衡策略"><a href="#负载均衡策略" class="headerlink" title="负载均衡策略"></a>负载均衡策略</h2><ul>
<li>轮询</li>
<li>weight round robbin  </li>
<li>random  </li>
<li>最少连接数（需要清楚服务端状态，属于动态负载均衡）</li>
<li>最快响应（需要记录不同机器上服务的响应速度，属于动态负载均衡）</li>
<li>hash(可以实现有状态的调度)</li>
</ul>
<p><img src="img/lb_algorithm.jpg" alt="lb_algorithm">  </p>
<h2 id="服务可用性探测"><a href="#服务可用性探测" class="headerlink" title="服务可用性探测"></a>服务可用性探测</h2><ul>
<li><p>HTTP探测</p>
<pre><code>使用Get/Post的方式请求服务端的某个固定的URL，判断返回的内容是否符合预期。一般使用Http状态码、response中的内容来判断。
</code></pre></li>
<li><p>TCP探测</p>
<pre><code>基于Tcp的三次握手机制来探测指定的IP + 端口(握手成功后马上发一个rst
请求断开连接［可以使用linger选项］)。最佳实践可以借鉴阿里云的SLB机制
值得注意的是，为了尽早释放连接，在三次握手结束后立马跟上RST来中断TCP连接。
</code></pre></li>
<li><p>UDP探测</p>
<pre><code>可能有部分应用使用的UDP协议。在此协议下可以通过报文来进行探测指定的IP + 端口。最佳实践同样可以借鉴阿里云的SLB机制
结果的判定方式是：在服务端没有返回任何信息的情况下，默认正常状态。否则会返回一个ICMP的报错信息。
</code></pre></li>
</ul>
<p>下面的几篇文章还不错，mark下：<br><a href="https://www.cnblogs.com/Zachary-Fan/archive/2018/10/08/LoadBalance.html" target="_blank" rel="external">分布式系统关注点——仅需这一篇，吃透「负载均衡」妥妥的</a><br><a href="https://www.cnblogs.com/Zachary-Fan/p/DoLoadBalance.html" target="_blank" rel="external">分布式系统关注点——「负载均衡」到底该如何实施？</a></p>

      
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    <article id="post-server-operation-cmd" class="article article-type-post" itemscope itemprop="blogPost">
  
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      <a href="/2018/12/23/server-operation-cmd/" class="article-date">
  	<time datetime="2018-12-23T13:02:13.000Z" itemprop="datePublished">2018-12-23</time>
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      <a class="article-title" href="/2018/12/23/server-operation-cmd/">服务器一些常用的运维命令</a>
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    <ol class="toc"><li class="toc-item toc-level-2"><a class="toc-link" href="#CPU"><span class="toc-text">CPU</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#Memory"><span class="toc-text">Memory</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#I-O"><span class="toc-text">I/O</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#查看某个进程的线程数"><span class="toc-text">查看某个进程的线程数</span></a></li></ol>
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        <h2 id="CPU"><a href="#CPU" class="headerlink" title="CPU"></a>CPU</h2><p>top -n N -d interval #查看cpu使用率前N高的进程，没个interval/s刷新显示<br>pidstat -u -p $pid update_interval #-u指的是Report CPU utilization<br>ps</p>
<h2 id="Memory"><a href="#Memory" class="headerlink" title="Memory"></a>Memory</h2><p>vmstat<br>cat /proc/meminfo ＃可以查看内存，swap分区等的使用情况<br>pidstat -r -p $pid update_interval #-r指的是Report page faults and memory  utilization.<br>ps</p>
<h2 id="I-O"><a href="#I-O" class="headerlink" title="I/O"></a>I/O</h2><p>iostat -d update_interval<br>pidstat -d -p $pid update_interval #-d指的是Report I/O statistics (kernels 2.6.20 and later only).  </p>
<h2 id="查看某个进程的线程数"><a href="#查看某个进程的线程数" class="headerlink" title="查看某个进程的线程数"></a>查看某个进程的线程数</h2><p>cat /proc/$pid/status |grep Thread<br>pstree -p $pid<br>ps -xH #可以进一步使用grep过滤</p>
<p>tips:<br>pidstat是个很好用的命令，详情请man pidstat查看  </p>

      
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    <article id="post-levelDB" class="article article-type-post" itemscope itemprop="blogPost">
  
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      <a href="/2018/10/14/levelDB/" class="article-date">
  	<time datetime="2018-10-14T12:48:15.000Z" itemprop="datePublished">2018-10-14</time>
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      <a class="article-title" href="/2018/10/14/levelDB/">levelDB</a>
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    <ol class="toc"><li class="toc-item toc-level-2"><a class="toc-link" href="#Reads-And-Writes"><span class="toc-text">Reads And Writes</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#Atomic-Update"><span class="toc-text">Atomic Update</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#Concurrency"><span class="toc-text">Concurrency</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#Iteration"><span class="toc-text">Iteration</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#Snapshots"><span class="toc-text">Snapshots</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#Slice"><span class="toc-text">Slice</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#Comparators"><span class="toc-text">Comparators</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#Performance"><span class="toc-text">Performance</span></a></li></ol>
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        <p>#levelDB简介<br>LevelDB is a fast key-value storage library written at Google that provides an ordered mapping from string keys to string values.</p>
<p>source code: <a href="https://github.com/google/leveldb/" target="_blank" rel="external">google/leveldb</a><br>具体特性参考上面的Github说明页。</p>
<p><a href="https://github.com/google/leveldb/blob/master/doc/index.md" target="_blank" rel="external">levelDB使用说明文档</a></p>
<p>#示例操作<br><figure class="highlight cpp"><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></pre></td><td class="code"><pre><div class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">"leveldb/db.h"</span></span></div><div class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">"leveldb/write_batch.h"</span></span></div><div class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;iostream&gt;</span></span></div><div class="line"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="built_in">std</span>;</div><div class="line"></div><div class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">()</span></span></div><div class="line">&#123;</div><div class="line">    leveldb::DB *db;</div><div class="line">    leveldb::Options options;</div><div class="line">    options.create_if_missing = <span class="literal">true</span>;</div><div class="line">    leveldb::Status status = leveldb::DB::Open(options, <span class="string">"/tmp/testdb"</span>, &amp;db);</div><div class="line">    assert(status.ok());</div><div class="line"></div><div class="line">    <span class="comment">//Reads And Writes</span></div><div class="line">    leveldb::Status s = db-&gt;Put(leveldb::WriteOptions(), <span class="string">"os"</span>, <span class="string">"mac os"</span>); </div><div class="line">    <span class="keyword">if</span>(!s.ok())</div><div class="line">    &#123;</div><div class="line">        <span class="built_in">cerr</span> &lt;&lt; s.ToString() &lt;&lt; <span class="built_in">endl</span>;  </div><div class="line">        <span class="keyword">delete</span> db; </div><div class="line">        <span class="keyword">return</span> <span class="number">-1</span>;</div><div class="line">    &#125;</div><div class="line">    <span class="built_in">string</span> value;</div><div class="line">    s = db-&gt;Get(leveldb::ReadOptions(), <span class="string">"os"</span>, &amp;value);</div><div class="line">    <span class="keyword">if</span>(!s.ok())</div><div class="line">    &#123;</div><div class="line">        <span class="keyword">delete</span> db;</div><div class="line">        <span class="keyword">return</span> <span class="number">-1</span>;</div><div class="line">    &#125;</div><div class="line"></div><div class="line">    <span class="built_in">cout</span> &lt;&lt; <span class="string">"os: "</span> &lt;&lt; value &lt;&lt; <span class="built_in">endl</span>;</div><div class="line"></div><div class="line">    <span class="comment">//Atomic Updates</span></div><div class="line">        </div><div class="line">    <span class="keyword">delete</span> db;</div><div class="line">    <span class="keyword">return</span> <span class="number">0</span>;</div><div class="line">&#125;</div></pre></td></tr></table></figure></p>
<p>#源码分析</p>
<h2 id="Reads-And-Writes"><a href="#Reads-And-Writes" class="headerlink" title="Reads And Writes"></a>Reads And Writes</h2><p>read – Get<br>Get操作支持区间查找’Approximate Sizes’  </p>
<figure class="highlight julia"><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">leveldb<span class="type">::</span><span class="built_in">Range</span> ranges[<span class="number">2</span>];</div><div class="line">ranges[<span class="number">0</span>] = leveldb<span class="type">::</span><span class="built_in">Range</span>(<span class="string">"a"</span>, <span class="string">"c"</span>);</div><div class="line">ranges[<span class="number">1</span>] = leveldb<span class="type">::</span><span class="built_in">Range</span>(<span class="string">"x"</span>, <span class="string">"z"</span>);</div><div class="line">uint64_t sizes[<span class="number">2</span>];</div><div class="line">leveldb<span class="type">::</span>Status s = db-&gt;GetApproximateSizes(ranges, <span class="number">2</span>, sizes);</div></pre></td></tr></table></figure>
<p>write – Put<br>其中Write操作又分为Synchronous Writes和asynchronous writes  </p>
<h2 id="Atomic-Update"><a href="#Atomic-Update" class="headerlink" title="Atomic Update"></a>Atomic Update</h2><p>使用leveldb::WriteBatch类实现  </p>
<h2 id="Concurrency"><a href="#Concurrency" class="headerlink" title="Concurrency"></a>Concurrency</h2><p>leveldb支持单进程中多线程的并发，不支持多进程之间的并发.</p>
<h2 id="Iteration"><a href="#Iteration" class="headerlink" title="Iteration"></a>Iteration</h2><p>迭代器遍历levelDB</p>
<h2 id="Snapshots"><a href="#Snapshots" class="headerlink" title="Snapshots"></a>Snapshots</h2><h2 id="Slice"><a href="#Slice" class="headerlink" title="Slice"></a>Slice</h2><p>leveldb存储类型的底层实现为一个Slice结构</p>
<h2 id="Comparators"><a href="#Comparators" class="headerlink" title="Comparators"></a>Comparators</h2><p>支持自定义Comparators来对k/v进行排序</p>
<h2 id="Performance"><a href="#Performance" class="headerlink" title="Performance"></a>Performance</h2><p>底层存储技术涉及memtable, sstable，Compression, Cache</p>
<p>##Filter </p>
<p>参考资料：<br><a href="https://www.cnblogs.com/liuhao/archive/2012/11/29/2795455.html" target="_blank" rel="external">LevelDB Cache实现机制分析</a></p>

      
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        <p>可以使用std::async来启动一个异步任务，其返回一个std::future对象。std::future对象最终将持有函数的返回值。当你需要这个值时，只要在future上调用get()，线程就会阻塞直到future就绪，返回该值。</p>
<figure class="highlight autoit"><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"><span class="built_in">int</span> <span class="function"><span class="keyword">func</span><span class="params">()</span>;</span></div><div class="line">std::future&lt;<span class="built_in">int</span>&gt; answer = std::async(<span class="function"><span class="keyword">func</span>);</span></div><div class="line">answer.get()<span class="comment">;</span></div></pre></td></tr></table></figure>

      
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        <h1 id="condtion-variable"><a href="#condtion-variable" class="headerlink" title="condtion_variable"></a>condtion_variable</h1><p>标准C+＋库提供了两个条件变量的实现：std::condition_variable和std::condition_variable_any。两者都需要和互斥元一起工作，以便提供恰当的同步。<br>以std::condition_variable为例，使用方法(以生产者消费者模型为例)如下：  </p>
<figure class="highlight cpp"><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></pre></td><td class="code"><pre><div class="line"><span class="built_in">std</span>:mutex <span class="number">_</span>mutex;</div><div class="line"><span class="built_in">std</span>::condition_variable data_cond;</div><div class="line"><span class="built_in">std</span>::<span class="built_in">queue</span>&lt;data_chunk&gt; data_queue;</div><div class="line"></div><div class="line"><span class="function"><span class="keyword">void</span> <span class="title">producer</span><span class="params">()</span></span></div><div class="line">&#123;</div><div class="line">	<span class="keyword">while</span>(<span class="number">1</span>)</div><div class="line">	&#123;</div><div class="line">		data_chunk <span class="keyword">const</span> data = prepare_data();</div><div class="line">		<span class="built_in">std</span>::lock_guard(<span class="built_in">std</span>::mutex) lg(<span class="number">_</span>mutex);</div><div class="line">		data_queue.push(data);</div><div class="line">		data_cond.notify_one();</div><div class="line">	&#125;</div><div class="line">&#125;</div><div class="line"></div><div class="line"><span class="function"><span class="keyword">void</span> <span class="title">comsumer</span><span class="params">()</span></span></div><div class="line">&#123;</div><div class="line">	<span class="keyword">while</span>(<span class="number">1</span>)</div><div class="line">	&#123;</div><div class="line">		<span class="built_in">std</span>::unique_lock&lt;<span class="built_in">std</span>::mutex&gt; uk(<span class="number">_</span>mutex);  <span class="comment">//condition_variable should be used with unique_lock</span></div><div class="line">		data_cond.wait(uk, []&#123;<span class="keyword">return</span> !data_queue.empty();&#125;)</div><div class="line">		</div><div class="line">		<span class="comment">//after wake up</span></div><div class="line">		data_chunk data=data_queue.front();</div><div class="line">		data_queue.pop();</div><div class="line">		uk.unlock();</div><div class="line">		process(data);</div><div class="line">	&#125;</div><div class="line">&#125;</div></pre></td></tr></table></figure>
<p>#share_mutex<br>对于写操作，使用std::lock_guard<boost:shared_mutex>和std::unique_lock<boost::shared_mutex>加写锁，进行独占访问。<br>对于读操作，使用boost::shared_lock<boost::shared_mutext> 加读锁，允许多个读者同时进行读取。</boost::shared_mutext></boost::shared_mutex></boost:shared_mutex></p>

      
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        <h1 id="lock-guard"><a href="#lock-guard" class="headerlink" title="lock_guard"></a>lock_guard</h1><p>std::lock_guard使用起来比较简单，其在构造函数中对std::mutex变量进行锁定，在其析构函数中对std::mutex变量进行解锁，整个类没有对mutex进行解锁和加锁的对外接口，其源码如下：</p>
<figure class="highlight arduino"><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"><span class="keyword">template</span> &lt;<span class="keyword">class</span> _Mutex&gt;</div><div class="line"><span class="keyword">class</span> _LIBCPP_TYPE_VIS_ONLY lock_guard</div><div class="line">&#123;</div><div class="line"><span class="keyword">public</span>:</div><div class="line">    <span class="keyword">typedef</span> _Mutex mutex_type;</div><div class="line"></div><div class="line"><span class="keyword">private</span>:</div><div class="line">    mutex_type&amp; __m_;</div><div class="line"><span class="keyword">public</span>:</div><div class="line"></div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    <span class="keyword">explicit</span> lock_guard(mutex_type&amp; __m)</div><div class="line">        : __m_(__m) &#123;__m_.lock();&#125;</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    lock_guard(mutex_type&amp; __m, adopt_lock_t)</div><div class="line">        : __m_(__m) &#123;&#125;</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    ~lock_guard() &#123;__m_.unlock();&#125;</div><div class="line"></div><div class="line"><span class="keyword">private</span>:</div><div class="line">    lock_guard(lock_guard <span class="keyword">const</span>&amp;);<span class="comment">// = delete;</span></div><div class="line">    lock_guard&amp; <span class="keyword">operator</span>=(lock_guard <span class="keyword">const</span>&amp;);<span class="comment">// = delete;</span></div><div class="line">&#125;;</div></pre></td></tr></table></figure>
<p>使用方法如下：  </p>
<figure class="highlight cpp"><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"><span class="built_in">std</span>::mutex g_mutex;</div><div class="line"><span class="keyword">int</span> g_var = <span class="number">0</span>;</div><div class="line"></div><div class="line"><span class="function"><span class="keyword">void</span> <span class="title">test_guard</span><span class="params">()</span></span></div><div class="line">&#123;</div><div class="line">    <span class="built_in">std</span>::lock_guard&lt;<span class="built_in">std</span>::mutex&gt; guard(g_mutex);</div><div class="line">    g_var ++;</div><div class="line">&#125;</div></pre></td></tr></table></figure>
<h1 id="unique-lock"><a href="#unique-lock" class="headerlink" title="unique_lock"></a>unique_lock</h1><p>unique_lock相比lock_guard，功能要多很多，其提供了对mutex的加锁（lock和try_lock）和解锁（unlock）操作，同时可以配合条件变量condition_variable使用：  </p>
<figure class="highlight arduino"><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><div class="line">50</div><div class="line">51</div><div class="line">52</div><div class="line">53</div><div class="line">54</div><div class="line">55</div><div class="line">56</div><div class="line">57</div><div class="line">58</div><div class="line">59</div><div class="line">60</div><div class="line">61</div><div class="line">62</div><div class="line">63</div><div class="line">64</div><div class="line">65</div><div class="line">66</div><div class="line">67</div><div class="line">68</div><div class="line">69</div><div class="line">70</div><div class="line">71</div><div class="line">72</div><div class="line">73</div><div class="line">74</div><div class="line">75</div><div class="line">76</div><div class="line">77</div><div class="line">78</div><div class="line">79</div><div class="line">80</div><div class="line">81</div><div class="line">82</div><div class="line">83</div><div class="line">84</div><div class="line">85</div><div class="line">86</div><div class="line">87</div><div class="line">88</div><div class="line">89</div><div class="line">90</div><div class="line">91</div><div class="line">92</div><div class="line">93</div><div class="line">94</div><div class="line">95</div><div class="line">96</div><div class="line">97</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">template</span> &lt;<span class="keyword">class</span> _Mutex&gt;</div><div class="line"><span class="keyword">class</span> _LIBCPP_TYPE_VIS_ONLY unique_lock</div><div class="line">&#123;</div><div class="line"><span class="keyword">public</span>:</div><div class="line">    <span class="keyword">typedef</span> _Mutex mutex_type;</div><div class="line"></div><div class="line"><span class="keyword">private</span>:</div><div class="line">    mutex_type* __m_;</div><div class="line">    <span class="keyword">bool</span> __owns_;</div><div class="line"></div><div class="line"><span class="keyword">public</span>:</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    unique_lock() _NOEXCEPT : __m_(nullptr), __owns_(false) &#123;&#125;</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    <span class="keyword">explicit</span> unique_lock(mutex_type&amp; __m)</div><div class="line">        : __m_(&amp;__m), __owns_(true) &#123;__m_-&gt;lock();&#125;</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    unique_lock(mutex_type&amp; __m, defer_lock_t) _NOEXCEPT</div><div class="line">        : __m_(&amp;__m), __owns_(false) &#123;&#125;</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    unique_lock(mutex_type&amp; __m, try_to_lock_t)</div><div class="line">        : __m_(&amp;__m), __owns_(__m.try_lock()) &#123;&#125;</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    unique_lock(mutex_type&amp; __m, adopt_lock_t)</div><div class="line">        : __m_(&amp;__m), __owns_(true) &#123;&#125;</div><div class="line">    <span class="keyword">template</span> &lt;<span class="keyword">class</span> _Clock, <span class="keyword">class</span> _Duration&gt;</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">        unique_lock(mutex_type&amp; __m, <span class="keyword">const</span> chrono::time_point&lt;_Clock, _Duration&gt;&amp; __t)</div><div class="line">            : __m_(&amp;__m), __owns_(__m.try_lock_until(__t)) &#123;&#125;</div><div class="line">    <span class="keyword">template</span> &lt;<span class="keyword">class</span> _Rep, <span class="keyword">class</span> _Period&gt;</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">        unique_lock(mutex_type&amp; __m, <span class="keyword">const</span> chrono::duration&lt;_Rep, _Period&gt;&amp; __d)</div><div class="line">            : __m_(&amp;__m), __owns_(__m.try_lock_for(__d)) &#123;&#125;</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    ~unique_lock()</div><div class="line">    &#123;</div><div class="line">        <span class="built_in">if</span> (__owns_)</div><div class="line">            __m_-&gt;unlock();</div><div class="line">    &#125;</div><div class="line"></div><div class="line"><span class="keyword">private</span>:</div><div class="line">    unique_lock(unique_lock <span class="keyword">const</span>&amp;); <span class="comment">// = delete;</span></div><div class="line">    unique_lock&amp; <span class="keyword">operator</span>=(unique_lock <span class="keyword">const</span>&amp;); <span class="comment">// = delete;</span></div><div class="line"></div><div class="line"><span class="keyword">public</span>:</div><div class="line"><span class="meta">#<span class="meta-keyword">ifndef</span> _LIBCPP_HAS_NO_RVALUE_REFERENCES</span></div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    unique_lock(unique_lock&amp;&amp; __u) _NOEXCEPT</div><div class="line">        : __m_(__u.__m_), __owns_(__u.__owns_)</div><div class="line">        &#123;__u.__m_ = nullptr; __u.__owns_ = false;&#125;</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    unique_lock&amp; <span class="keyword">operator</span>=(unique_lock&amp;&amp; __u) _NOEXCEPT</div><div class="line">        &#123;</div><div class="line">            <span class="built_in">if</span> (__owns_)</div><div class="line">                __m_-&gt;unlock();</div><div class="line">            __m_ = __u.__m_;</div><div class="line">            __owns_ = __u.__owns_;</div><div class="line">            __u.__m_ = nullptr;</div><div class="line">            __u.__owns_ = false;</div><div class="line">            <span class="built_in">return</span> *<span class="keyword">this</span>;</div><div class="line">        &#125;</div><div class="line"></div><div class="line"><span class="meta">#<span class="meta-keyword">endif</span>  <span class="comment">// _LIBCPP_HAS_NO_RVALUE_REFERENCES</span></span></div><div class="line"></div><div class="line">    <span class="keyword">void</span> lock();</div><div class="line">    <span class="keyword">bool</span> try_lock();</div><div class="line"></div><div class="line">    <span class="keyword">template</span> &lt;<span class="keyword">class</span> _Rep, <span class="keyword">class</span> _Period&gt;</div><div class="line">        <span class="keyword">bool</span> try_lock_for(<span class="keyword">const</span> chrono::duration&lt;_Rep, _Period&gt;&amp; __d);</div><div class="line">    <span class="keyword">template</span> &lt;<span class="keyword">class</span> _Clock, <span class="keyword">class</span> _Duration&gt;</div><div class="line">        <span class="keyword">bool</span> try_lock_until(<span class="keyword">const</span> chrono::time_point&lt;_Clock, _Duration&gt;&amp; __t);</div><div class="line"></div><div class="line">    <span class="keyword">void</span> unlock();</div><div class="line"></div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    <span class="keyword">void</span> swap(unique_lock&amp; __u) _NOEXCEPT</div><div class="line">    &#123;</div><div class="line">        _VSTD::swap(__m_, __u.__m_);</div><div class="line">        _VSTD::swap(__owns_, __u.__owns_);</div><div class="line">    &#125;</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    mutex_type* <span class="built_in">release</span>() _NOEXCEPT</div><div class="line">    &#123;</div><div class="line">        mutex_type* __m = __m_;</div><div class="line">        __m_ = nullptr;</div><div class="line">        __owns_ = false;</div><div class="line">        <span class="built_in">return</span> __m;</div><div class="line">    &#125;</div><div class="line"></div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    <span class="keyword">bool</span> owns_lock() <span class="keyword">const</span> _NOEXCEPT &#123;<span class="built_in">return</span> __owns_;&#125;</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    _LIBCPP_EXPLICIT</div><div class="line">        <span class="keyword">operator</span> <span class="keyword">bool</span> () <span class="keyword">const</span> _NOEXCEPT &#123;<span class="built_in">return</span> __owns_;&#125;</div><div class="line">    _LIBCPP_INLINE_VISIBILITY</div><div class="line">    mutex_type* mutex() <span class="keyword">const</span> _NOEXCEPT &#123;<span class="built_in">return</span> __m_;&#125;</div><div class="line">&#125;;</div></pre></td></tr></table></figure>
<h1 id="unique-lock和lock-guard的区别"><a href="#unique-lock和lock-guard的区别" class="headerlink" title="unique_lock和lock_guard的区别"></a>unique_lock和lock_guard的区别</h1><p>简单的说，unique_lock相对于lock_guard,会有更多特性。<br>unique_lock和lock_guard都遵循RAII。</p>
<p>unique_lock和lock_guard最大的不同是unique_lock不需要始终拥有关联的mutex，而lock_guard始终拥有mutex。这意味着unique_lock需要利用owns_lock()判断是否拥有mutex。另外，如果要结合使用条件变量，应该使用unique_lock。</p>
<p>Lock doesn’t have to taken right at the construction, you can pass the flag std::defer_lock during its construction to keep the mutex unlocked during construction.</p>
<p>We can unlock it before the function ends and don’t have to necessarily wait for destructor to release it, which can be handy.</p>
<p>You can pass the ownership of the lock from a function, it is movable and not copyable.</p>
<p>It can be used with conditional variables since that requires mutex to be locked, condition checked and unlocked while waiting for a condition.<br>参考[StackOverflow]:<a href="https://stackoverflow.com/questions/6731027/boostunique-lock-vs-boostlock-guard" target="_blank" rel="external">https://stackoverflow.com/questions/6731027/boostunique-lock-vs-boostlock-guard</a></p>
<p>#使用建议和说明<br>如果只是在某个区间进行简单的对象互斥访问的话，建议使用unique_gurad,这个比unique_lock来的更高效；如果在操作过程中涉及对锁对象的解锁和加锁操作的话，或者是使用了条件变量的情况下，使用uique_lock才能满足你的要求。</p>

      
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        <p>#下载与安装<br>参考github上的下载和安装说明： <a href="https://github.com/yaml/libyaml" target="_blank" rel="external">Canonical source repository for LibYAML</a><br>说明：<br>如果安装过程中出现 <strong><em> autoreconf: not found </em></strong> 错误的话，是由于automake未安装导致，mac<br>下的解决方法如下: <a href="https://www.jianshu.com/p/d5bf5a5a3436" target="_blank" rel="external">Mac 安装 automake</a>  </p>
<p>#使用说明<br><a href="https://github.com/tlsa/libcyaml" target="_blank" rel="external">C library for reading and writing YAML.</a></p>

      
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    <article id="post-distributed_system/concurrent-of-distribute-system" class="article article-type-post" itemscope itemprop="blogPost">
  
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        <p>1、数据库锁<br>根据事务的隔离性，调整不同的锁粒度（对行，数据块或表进行加锁）<br>2、写时复制COW<br>原理：对于写操作单独复制一份B+树丛叶子节点到根节点的路径，修改后再切换复制节点的根节点指向。具体步骤如下：  </p>
<ul>
<li>拷贝：将从叶子到根节点路径上的所有节点拷贝一份  </li>
<li>修改：基于拷贝的节点进行修改  </li>
<li>提交：原子地切换根节点的指针，使之指向新的根节点（同时旧的节点会根据维护的引用计数情况是否为0，觉得是否进行垃圾回收）<br>优点：读操作不用加锁，极大提升了读取性能<br>缺点：每次写操作都需要拷贝从叶子到根结点路径上的所有节点，写操作成本高；另外，不支持多个写操作并发  </li>
</ul>
<p>3、多版本MVCC<br>原理：对每行数据维护多个版本，无论事务的执行时间有多长，MVCC总是能够提供与事务开始时刻相一致的数据。实际是增加了俩个隐式列：行被修改的”时间”和行被删除的”时间”（这个时间实际上是一个递增的唯一事务号）。对于每一次查询，会把当前事务的事务号同行存储的事务号进行对比，然后结合不同的事务隔离级别，来决定是否返回该行。<br>优点：<br>读取数据不需要加锁，每个读事务只获取自己的事务版本，大大提高了并发度；可以支持多个写事务并发<br>缺点：<br>需要额外存储多个版本数据；需对多个版本数据进行维护，定时删除不需要的版本，回收空间<br>根据这个原理，select/delete/update/insert语句的行为如下：  </p>
<ul>
<li>select<br>进行select操作时需要满足，才能返回数据<br>1) 行的修改版本号小于等于该事务号<br>2) 行的删除版本号要么没定义，要么大于事务的版本号(表示数据在未来被其他事务删除)  </li>
<li>delete<br>更改行的删除版本号为当前事务号  </li>
<li>update<br>将原来的行复制一份，更改行的修改版本号为当前事务号  </li>
<li>insert<br>设置行的修改版本号为当前事务号  </li>
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    <ol class="toc"><li class="toc-item toc-level-2"><a class="toc-link" href="#分类"><span class="toc-text">分类</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#存储引擎"><span class="toc-text">存储引擎</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#索引分类"><span class="toc-text">索引分类</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#容错和故障恢复"><span class="toc-text">容错和故障恢复</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#负载均衡"><span class="toc-text">负载均衡</span></a></li></ol>
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        <h2 id="分类"><a href="#分类" class="headerlink" title="分类"></a>分类</h2><p>根据处理数据类型划分：<br>-分布式文件系统：非结构化数据<br>-分布式键值(K-V)：半结构化数据，分布式键值系统是分布式表格系统的简化实现<br>-分布式表格：半结构化数据<br>-分布式数据库：结构化数据</p>
<h2 id="存储引擎"><a href="#存储引擎" class="headerlink" title="存储引擎"></a>存储引擎</h2><p>哈希存储引擎：Bitcask<br>B-树存储引擎：InnoDB MySQL</p>
<h2 id="索引分类"><a href="#索引分类" class="headerlink" title="索引分类"></a>索引分类</h2><p>聚集索引</p>
<p>一级索引和二级索引</p>
<h2 id="容错和故障恢复"><a href="#容错和故障恢复" class="headerlink" title="容错和故障恢复"></a>容错和故障恢复</h2><p> P37 故障恢复<br> 容错方式：Master-slave架构<br> Data Server数据备份</p>
<h2 id="负载均衡"><a href="#负载均衡" class="headerlink" title="负载均衡"></a>负载均衡</h2><p>负载均衡软件：<br>LVS<br>Haproxy<br>分级存储：合理利用SSD/SAS/SATA磁盘<br>功耗：I/O密集型和CPU密集型<br>计算数据的hash值，然后分布到不同的bucket中</p>
<p>思维导向图工具<br>向量时钟<br>数据回传<br>Merkle树<br>冲突处理等复杂的P2P技术</p>
<p>paxos数据复制<br>俩阶段提交协议？<br>LinuxHA软件？实现高可用<br>Zookeeper协议</p>

      
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    <ol class="toc"><li class="toc-item toc-level-2"><a class="toc-link" href="#内核待机和唤醒代码分布"><span class="toc-text">内核待机和唤醒代码分布</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#待机及唤醒流程分析"><span class="toc-text">待机及唤醒流程分析</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#如何统计模块唤醒时长"><span class="toc-text">如何统计模块唤醒时长</span></a></li></ol>
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        <h2 id="内核待机和唤醒代码分布"><a href="#内核待机和唤醒代码分布" class="headerlink" title="内核待机和唤醒代码分布"></a>内核待机和唤醒代码分布</h2><ol>
<li>kernel/power  </li>
<li>drivers/base/power  </li>
</ol>
<h2 id="待机及唤醒流程分析"><a href="#待机及唤醒流程分析" class="headerlink" title="待机及唤醒流程分析"></a>待机及唤醒流程分析</h2><p>可以查看我的csdn博客<a href="https://blog.csdn.net/CODINGCS/article/details/80148069" target="_blank" rel="external">Linux Kernel and Android 休眠与唤醒(中文版)</a></p>
<h2 id="如何统计模块唤醒时长"><a href="#如何统计模块唤醒时长" class="headerlink" title="如何统计模块唤醒时长"></a>如何统计模块唤醒时长</h2><p>废话不多说，直接贴代码：</p>
<p>drivers/base/power/main.c</p>
<figure class="highlight pf"><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></pre></td><td class="code"><pre><div class="line">static int dpm_run_callback(pm_callback_t cb, struct device *dev,</div><div class="line">			    pm_message_t <span class="keyword">state</span>, char *info)</div><div class="line">&#123;</div><div class="line">	ktime_t calltime;</div><div class="line">	int error;</div><div class="line"></div><div class="line">	if (!cb)</div><div class="line">		return <span class="number">0</span>;</div><div class="line"></div><div class="line">	calltime = initcall_debug_start(dev);</div><div class="line"></div><div class="line">	pm_dev_dbg(dev, <span class="keyword">state</span>, info);</div><div class="line">	trace_device_pm_callback_start(dev, info, <span class="keyword">state</span>.event);</div><div class="line">	error = cb(dev);</div><div class="line">	trace_device_pm_callback_end(dev, error);</div><div class="line">	suspend_report_result(cb, error);</div><div class="line"></div><div class="line">	initcall_debug_report(dev, calltime, error, <span class="keyword">state</span>, info);</div><div class="line"></div><div class="line">	return error;</div><div class="line">&#125;</div></pre></td></tr></table></figure>
<p>具体看下initcall_debug_start及initcall_debug_report两个函数的定义：</p>
<figure class="highlight cpp"><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></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">static</span> ktime_t <span class="title">initcall_debug_start</span><span class="params">(<span class="keyword">struct</span> device *dev)</span></span></div><div class="line">&#123;</div><div class="line">	<span class="keyword">ktime_t</span> calltime = ktime_set(<span class="number">0</span>, <span class="number">0</span>);</div><div class="line"></div><div class="line">	<span class="keyword">if</span> (pm_print_times_enabled) &#123;</div><div class="line">		pr_info(<span class="string">"calling  %s+ @ %i, parent: %s\n"</span>,</div><div class="line">			dev_name(dev), task_pid_nr(current),</div><div class="line">			dev-&gt;parent ? dev_name(dev-&gt;parent) : <span class="string">"none"</span>);</div><div class="line">		calltime = ktime_get();</div><div class="line">	&#125;</div><div class="line"></div><div class="line">	<span class="keyword">return</span> calltime;</div><div class="line">&#125;</div><div class="line"></div><div class="line"><span class="function"><span class="keyword">static</span> <span class="keyword">void</span> <span class="title">initcall_debug_report</span><span class="params">(<span class="keyword">struct</span> device *dev, <span class="keyword">ktime_t</span> calltime,</span></span></div><div class="line">				  <span class="keyword">int</span> error, <span class="keyword">pm_message_t</span> state, <span class="keyword">char</span> *info)</div><div class="line">&#123;</div><div class="line">	<span class="keyword">ktime_t</span> rettime;</div><div class="line">	s64 nsecs;</div><div class="line"></div><div class="line">	rettime = ktime_get();</div><div class="line">	nsecs = (s64) ktime_to_ns(ktime_sub(rettime, calltime));</div><div class="line"></div><div class="line">	<span class="keyword">if</span> (pm_print_times_enabled) &#123;</div><div class="line">		pr_info(<span class="string">"call %s+ returned %d after %Ld usecs\n"</span>, dev_name(dev),</div><div class="line">			error, (<span class="keyword">unsigned</span> <span class="keyword">long</span> <span class="keyword">long</span>)nsecs &gt;&gt; <span class="number">10</span>);</div><div class="line">	&#125;</div><div class="line">&#125;</div></pre></td></tr></table></figure>

      
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