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| <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav> <ul class="sidebar-links"><li><section class="sidebar-group depth-0"><p class="sidebar-heading"><span>系统设计</span> <!----></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>应用概览</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>TsFile</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>查询引擎</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>元数据管理</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>存储引擎</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>数据查询</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/zh/SystemDesign/DataQuery/DataQuery.html" class="sidebar-link">数据查询</a></li><li><a href="/zh/SystemDesign/DataQuery/QueryFundamentals.html" class="sidebar-link">查询基础介绍</a></li><li><a href="/zh/SystemDesign/DataQuery/SeriesReader.html" class="sidebar-link">查询基础组件</a></li><li><a href="/zh/SystemDesign/DataQuery/RawDataQuery.html" class="sidebar-link">原始数据查询</a></li><li><a href="/zh/SystemDesign/DataQuery/AggregationQuery.html" class="sidebar-link">聚合查询</a></li><li><a href="/zh/SystemDesign/DataQuery/GroupByQuery.html" class="sidebar-link">降采样查询</a></li><li><a href="/zh/SystemDesign/DataQuery/LastQuery.html" class="sidebar-link">最近时间戳 Last 查询</a></li><li><a href="/zh/SystemDesign/DataQuery/AlignByDeviceQuery.html" class="sidebar-link">按设备对齐查询</a></li><li><a href="/zh/SystemDesign/DataQuery/FillFunction.html" class="sidebar-link">空值填充</a></li><li><a href="/zh/SystemDesign/DataQuery/GroupByFillQuery.html" class="sidebar-link">降采样补空值查询</a></li><li><a href="/zh/SystemDesign/DataQuery/OrderByTimeQuery.html" aria-current="page" class="active sidebar-link">按时间倒序查询</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>工具</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>连接器</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>客户端</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <main class="page"> <div class="content content__default"><h1 id="按时间倒序查询"><a href="#按时间倒序查询" class="header-anchor">#</a> 按时间倒序查询</h1> <h2 id="实现原理"><a href="#实现原理" class="header-anchor">#</a> 实现原理</h2> <p>倒序分为 3 个维度来实现，由内核层到用户层分别为: <code>TsFile</code>、<code>BatchData</code>、<code>数据集</code>.</p> <ol><li><code>TsFile</code> 是用来存储所有原始数据的文件格式，在存储时分为 <code>顺序文件</code> 和 <code>乱序文件</code>. |
| <code>ChunkData</code> 是 <code>TsFile</code> 中的基本数据块，保存了具体某一个测点的数据，且<strong>数据是按照时间升序存储的</strong>.</li> <li><code>BatchData</code> 是基础数据交换结构，无论是从文件系统还是缓存读出的数据都会被转换成 <code>BatchData</code> 结构.</li> <li><code>数据集</code> 是封装根据用户输入的 <code>SQL</code> 语句的结果集格式，转换和封装 <code>BatchData</code> 中的数据。</li></ol> <p>实际系统需要考虑的方面会更多，但主要为以上 3 点。 |
| 下面分别介绍各个层面如何实现基于时间的倒序查询:</p> <h2 id="tsfile"><a href="#tsfile" class="header-anchor">#</a> TsFile</h2> <p>1.<code>TsFile</code> 在文件末尾存储了各个测点在文件中的最小时间(开始时间)和最大时间(结束时间)， |
| 所以当我们按照开始时间升序排列文件并读取数据时,是升序读取;当使用结束时间倒序排列文件 |
| (<strong>顺序文件也可以使用开始时间倒序排列</strong>)并读取数据时,是<strong>伪倒序读取</strong>(因为文件内依然是升序存储的),数据示例:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code> 按照开始时间升序排列 (1,6) |
| +---TsFile1---+ +---TsFile2---+ |
| | 1,2,3,4,5 | | 6,7,8,9,10 | |
| +-------------+ +-------------+ |
| |
| 按照结束降序排列 (10,5) |
| +---TsFile2---+ +---TsFile1---+ |
| | 6,7,8,9,10 | | 1,2,3,4,5 | |
| +-------------+ +-------------+ |
| </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><p>2.上面的示例只描述了顺序文件，乱序文件的特点是: 文件中存储的数据与其他文件的数据存在相交， |
| 不仅仅和顺序文件相交，乱序和乱序文件之间也可能相交。</p> <div class="language- line-numbers-mode"><pre class="language-text"><code> +---TsFile1---+ +---TsFile2---+ |
| | 1,2,3,4,5 | | 6,7,8,9,10 | |
| +-------------+ +-------------+ |
| +--------------unseq1-----------+ |
| | 2,11 | |
| +-------------------------------+ |
| +-unseq2-+ |
| | 3,4,5 | |
| +--------+ |
| |
| </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br></div></div><p>3.对于<strong>相交</strong>的部分，需要使用<code>多路归并</code>查询出最终结果。具体处理细节可以参见<a href="/zh/SystemDesign/DataQuery/SeriesReader.html">SeriesReader</a>.</p> <p>4.对于文件层而言，我们抽象出了<code>TimeOrderUtils</code>，用来完成对升序、降序不同实现的方法提取。</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code> <span class="token keyword">public</span> <span class="token keyword">interface</span> <span class="token class-name">TimeOrderUtils</span> <span class="token punctuation">{</span> |
| <span class="token comment">//排序使用的字段，升序使用开始时间，降序使用结束时间。</span> |
| <span class="token comment">//TsFileResource面对文件相关，Statistics面向Chunk和Page相关</span> |
| <span class="token keyword">long</span> <span class="token function">getOrderTime</span><span class="token punctuation">(</span><span class="token class-name">Statistics</span> statistics<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| <span class="token keyword">long</span> <span class="token function">getOrderTime</span><span class="token punctuation">(</span><span class="token class-name">TsFileResource</span> fileResource<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| |
| <span class="token comment">//判断是否相交使用的时间依据，升序使用结束时间，降序使用开始时间</span> |
| <span class="token keyword">long</span> <span class="token function">getOverlapCheckTime</span><span class="token punctuation">(</span><span class="token class-name">Statistics</span> range<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| |
| <span class="token comment">//根据提供的时间判断是否相交，left为依据时间，right为要判断的文件</span> |
| <span class="token keyword">boolean</span> <span class="token function">isOverlapped</span><span class="token punctuation">(</span><span class="token class-name">Statistics</span> left<span class="token punctuation">,</span> <span class="token class-name">Statistics</span> right<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| <span class="token keyword">boolean</span> <span class="token function">isOverlapped</span><span class="token punctuation">(</span><span class="token keyword">long</span> time<span class="token punctuation">,</span> <span class="token class-name">Statistics</span> right<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| <span class="token keyword">boolean</span> <span class="token function">isOverlapped</span><span class="token punctuation">(</span><span class="token keyword">long</span> time<span class="token punctuation">,</span> <span class="token class-name">TsFileResource</span> right<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| |
| <span class="token comment">//对于有序文件的遍历规则，升序时正序遍历，降序时倒序遍历</span> |
| <span class="token class-name">TsFileResource</span> <span class="token function">getNextSeqFileResource</span><span class="token punctuation">(</span><span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">TsFileResource</span><span class="token punctuation">></span></span> seqResources<span class="token punctuation">,</span> <span class="token keyword">boolean</span> isDelete<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| |
| <span class="token comment">//对于所有文件层的临时缓存排序规则的实现</span> |
| <span class="token generics"><span class="token punctuation"><</span><span class="token class-name">T</span><span class="token punctuation">></span></span> <span class="token class-name">Comparator</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">T</span><span class="token punctuation">></span></span> <span class="token function">comparingLong</span><span class="token punctuation">(</span><span class="token class-name">ToLongFunction</span><span class="token generics"><span class="token punctuation"><</span><span class="token operator">?</span> <span class="token keyword">super</span> <span class="token class-name">T</span><span class="token punctuation">></span></span> keyExtractor<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| |
| <span class="token comment">//循环读取数据时判断是否到达了当前设置的停止点</span> |
| <span class="token keyword">boolean</span> <span class="token function">isExcessEndpoint</span><span class="token punctuation">(</span><span class="token keyword">long</span> time<span class="token punctuation">,</span> <span class="token keyword">long</span> endpointTime<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| |
| <span class="token comment">//或许当前使用的排序方式</span> |
| <span class="token keyword">boolean</span> <span class="token function">getAscending</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> |
| <span class="token punctuation">}</span> |
| </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br></div></div><p>5.完成了上述步骤，倒序取出来的数据如下：</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>6,7,8,9,10,1,2,3,4,5 |
| </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>这是因为数据在Chunk、Page、缓存中都是升序存储，所以转移到 <code>BatchData</code> 中查看就是示例中的样子。</p> <h2 id="batchdata"><a href="#batchdata" class="header-anchor">#</a> BatchData</h2> <p>1.为了兼容原有的文件读取数据方式，所以在数据放到 <code>BatchData</code> 之后倒序读取集合里的数据就可以得到最终结果。</p> <p>BatchData类似一个二维数组的格式，封装了写入和读取的方法，对于倒序，抽象了下面的子类：</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code> |
| <span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">DescBatchData</span> <span class="token keyword">extends</span> <span class="token class-name">BatchData</span> <span class="token punctuation">{</span> |
| <span class="token comment">//判断是否还有值，正序时候判断是否读到写入的size位置，倒序就是判断是否读到了0的位置</span> |
| <span class="token keyword">public</span> <span class="token keyword">boolean</span> <span class="token function">hasCurrent</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> |
| <span class="token comment">//指针移动到下一个数据，正序为 index+1 操作， 倒序为 index-1 操作</span> |
| <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">next</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> |
| <span class="token comment">//重制指针位置，正序为重制到0，倒序重制到数据写入位置</span> |
| <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">resetBatchData</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> |
| <span class="token comment">//就像是Nio中的Buffer类的flip操作，在数据写入完成时做的操作，为读取做好准备</span> |
| <span class="token keyword">public</span> <span class="token class-name">BatchData</span> <span class="token function">flip</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> |
| <span class="token comment">//使用具体时间获取值，正序时index从0到size遍历，倒序时从size到0遍历</span> |
| <span class="token keyword">public</span> <span class="token class-name">Object</span> <span class="token function">getValueInTimestamp</span><span class="token punctuation">(</span><span class="token keyword">long</span> time<span class="token punctuation">)</span><span class="token punctuation">;</span> |
| <span class="token punctuation">}</span> |
| </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><p>2.在需要倒序处理数据的位置构建<code>DescBatchData</code>类，为此，特意设计了一个<code>BatchDataFactory</code>类， |
| 根据ascending参数判断生产哪个类型的BatchData。</p> <p>3.因为<code>MergeReader</code>使用了<code>PageReader</code>，所以在降序模式的时候数据会被倒序读出来(如下):</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>5 4 3 2 1 |
| </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>这种情况会使得<code>BatchData</code>使用<code>getValueInTimestamp</code>方法变得困难(因为在正序模式的时候默认为越往后的数据时间越大， |
| 倒序模式的时候越后时间越小)，但是按照如上数据示例无论在哪种模式下，都是违反了期望的数据时间比较，所以，新增了一个 |
| <code>getValueInTimestamp(long time, BiFunction<Long, Long, Boolean> compare)</code>方法， |
| 让不同的使用场景抉择基于时间的数据查找方式。</p> <p>4.至此数据从磁盘和缓存中取出的数据都是严格按照时间排序的了。</p> <h2 id="数据集"><a href="#数据集" class="header-anchor">#</a> 数据集</h2> <p>1.原始数据查询</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> <span class="token operator">*</span> <span class="token keyword">from</span> root <span class="token keyword">order</span> <span class="token keyword">by</span> <span class="token keyword">time</span> <span class="token keyword">desc</span> |
| <span class="token keyword">select</span> <span class="token operator">*</span> <span class="token keyword">from</span> root <span class="token keyword">where</span> root<span class="token punctuation">.</span>ln<span class="token punctuation">.</span>d1<span class="token punctuation">.</span>s1<span class="token operator">></span><span class="token number">100</span> <span class="token keyword">order</span> <span class="token keyword">by</span> <span class="token keyword">time</span> <span class="token keyword">desc</span> |
| <span class="token keyword">select</span> <span class="token operator">*</span> <span class="token keyword">from</span> root <span class="token keyword">where</span> <span class="token keyword">time</span> <span class="token operator">></span><span class="token number">100</span> <span class="token keyword">order</span> <span class="token keyword">by</span> <span class="token keyword">time</span> <span class="token keyword">desc</span> |
| </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>原始数据查询中，只要向<code>SeriesReader</code>传递了正确的ascending参数就能得到正确的结果。</p> <p>2.GroupBy</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> max_time<span class="token punctuation">(</span><span class="token operator">*</span><span class="token punctuation">)</span> <span class="token keyword">from</span> root <span class="token keyword">group</span> <span class="token keyword">by</span> <span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span><span class="token number">10</span><span class="token punctuation">]</span><span class="token punctuation">,</span><span class="token number">2</span>ms<span class="token punctuation">)</span> <span class="token keyword">order</span> <span class="token keyword">by</span> <span class="token keyword">time</span> <span class="token keyword">desc</span> |
| </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>如上所示的Sql中,groupBy查询的区间分别为:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>[0-2),[2-4),[4-6),[6-8),[8-10) |
| </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>倒序查询只需要将时间计算的过程修改为:</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>[8-10),[6-8),[4-6),[2-4),[0-2) |
| </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><blockquote><p>计算方法为:</p> <p>((结束时间-开始时间)/步长值） 结果向上取整，得到的值为GroupBy中会发生的遍历次数(记为i)。</p> <p>(步长 * (i-1) + 开始时间) 结果为第i次遍历的开始时间值。</p></blockquote> <p>对于BatchData中的数据大于每次遍历的结束时间时，进行skip，然后对 <code>AggregateResult</code> 新增 |
| minBound计算限制,限制为第i次遍历的开始时间值， |
| <strong>数据无论是正序还是倒序遍历对于<code>AggregateResult</code>的结果是等价的</strong>.</p> <p>3.GroupByFill</p> <div class="language-sql line-numbers-mode"><pre class="language-sql"><code><span class="token keyword">select</span> last_value<span class="token punctuation">(</span>s0<span class="token punctuation">)</span> <span class="token keyword">from</span> root<span class="token punctuation">.</span>ln<span class="token punctuation">.</span>d1 <span class="token keyword">group</span> <span class="token keyword">by</span> <span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span><span class="token number">5</span><span class="token punctuation">]</span><span class="token punctuation">,</span><span class="token number">1</span>ms<span class="token punctuation">)</span> fill <span class="token punctuation">(</span>int32<span class="token punctuation">[</span>Previous<span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token keyword">order</span> <span class="token keyword">by</span> <span class="token keyword">time</span> <span class="token keyword">desc</span> |
| </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>对于升序的插值计算, 在 <code>GroupByFillDataSet</code> 中做了前值缓存，当本次查询的值不为空时，更新缓存; |
| 为空时使用缓存中的数据。</p> <p>对于降序查询，因为数据在倒序遍历，并不知道它的前值是多少，所以为 <code>GroupByEngineDataSet</code> |
| 抽象了 <code>peekNextNotNullValue</code> 方法，继续往前执行，一直查找到一个不为空的值返回。并将该值缓存到 |
| <code>GroupByFillDataSet</code> 中并遵从升序的补值方法，到当前的循环开始时间小于缓存的时间时缓存失效。</p> <p>4.Last |
| 在<code>LastQueryExecutor</code>中，一次性将所有的结果集封装在了一个List中， |
| 当倒序时将List中的数据根据时间进行一次排序,就得到了结果,详情见<code>ListDataSet</code>.</p></div> <div class="page-nav"><p class="inner"><span class="prev"> |
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