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| GitHub |
| <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" aria-current="page" class="active 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" class="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="查询基础组件"><a href="#查询基础组件" class="header-anchor">#</a> 查询基础组件</h1> <h2 id="设计原理"><a href="#设计原理" class="header-anchor">#</a> 设计原理</h2> <p>IoTDB server 模块共提供 3 种不同形式的针对单个时间序列的读取接口，以支持不同形式的查询。</p> <ul><li>原始数据查询接口，返回 BatchData，可带时间过滤条件或值过滤条件，两种过滤不可同时存在。</li> <li>聚合查询接口 （主要用于聚合查询和降采样查询）</li> <li>按递增时间戳查询对应值的接口（主要用于带值过滤的查询）</li></ul> <h2 id="相关接口"><a href="#相关接口" class="header-anchor">#</a> 相关接口</h2> <p>以上三种读取单个时间序列数据的方式对应代码里的三个接口</p> <h3 id="org-apache-iotdb-tsfile-read-reader-ibatchreader"><a href="#org-apache-iotdb-tsfile-read-reader-ibatchreader" class="header-anchor">#</a> org.apache.iotdb.tsfile.read.reader.IBatchReader</h3> <h4 id="主要方法"><a href="#主要方法" class="header-anchor">#</a> 主要方法</h4> <div class="language- line-numbers-mode"><pre class="language-text"><code>// 判断是否还有 BatchData |
| boolean hasNextBatch() throws IOException; |
| |
| // 获得下一个 BatchData，并把游标后移 |
| BatchData nextBatch() throws IOException; |
| </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></div></div><h4 id="使用流程"><a href="#使用流程" class="header-anchor">#</a> 使用流程</h4> <div class="language- line-numbers-mode"><pre class="language-text"><code>while (batchReader.hasNextBatch()) { |
| BatchData batchData = batchReader.nextBatch(); |
| |
| // use batchData to do some work |
| ... |
| } |
| </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></div></div><h3 id="org-apache-iotdb-db-query-reader-series-iaggregatereader"><a href="#org-apache-iotdb-db-query-reader-series-iaggregatereader" class="header-anchor">#</a> org.apache.iotdb.db.query.reader.series.IAggregateReader</h3> <h4 id="主要方法-2"><a href="#主要方法-2" class="header-anchor">#</a> 主要方法</h4> <div class="language- line-numbers-mode"><pre class="language-text"><code>// 判断是否还有 Chunk |
| boolean hasNextChunk() throws IOException; |
| |
| // 判断是否能够使用当前 Chunk 的统计信息 |
| boolean canUseCurrentChunkStatistics(); |
| |
| // 获得当前 Chunk 的统计信息 |
| Statistics currentChunkStatistics(); |
| |
| // 跳过当前 Chunk |
| void skipCurrentChunk(); |
| |
| // 判断当前Chunk是否还有下一个 Page |
| boolean hasNextPage() throws IOException; |
| |
| // 判断能否使用当前 Page 的统计信息 |
| boolean canUseCurrentPageStatistics() throws IOException; |
| |
| // 获得当前 Page 的统计信息 |
| Statistics currentPageStatistics() throws IOException; |
| |
| // 跳过当前的 Page |
| void skipCurrentPage(); |
| |
| // 获得当前 Page 的数据 |
| BatchData nextPage() throws IOException; |
| </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><h4 id="一般使用流程"><a href="#一般使用流程" class="header-anchor">#</a> 一般使用流程</h4> <div class="language- line-numbers-mode"><pre class="language-text"><code>while (aggregateReader.hasNextChunk()) { |
| if (aggregateReader.canUseCurrentChunkStatistics()) { |
| Statistics chunkStatistics = aggregateReader.currentChunkStatistics(); |
| |
| // 用 chunk 层的统计信息计算 |
| ... |
| |
| aggregateReader.skipCurrentChunk(); |
| continue; |
| } |
| |
| // 把当前 chunk 中的 page 消耗完 |
| while (aggregateReader.hasNextPage()) { |
| if (aggregateReader.canUseCurrentPageStatistics()) { |
| // 可以用统计信息 |
| Statistics pageStatistic = aggregateReader.currentPageStatistics(); |
| |
| // 用 page 层的统计信息计算 |
| ... |
| |
| aggregateReader.skipCurrentPage(); |
| continue; |
| } else { |
| // 不能用统计信息，需要用数据计算 |
| BatchData batchData = aggregateReader.nextOverlappedPage(); |
| |
| // 用 batchData 计算 |
| ... |
| } |
| } |
| } |
| </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><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br></div></div><h3 id="org-apache-iotdb-db-query-reader-ireaderbytimestamp"><a href="#org-apache-iotdb-db-query-reader-ireaderbytimestamp" class="header-anchor">#</a> org.apache.iotdb.db.query.reader.IReaderByTimestamp</h3> <h4 id="主要方法-3"><a href="#主要方法-3" class="header-anchor">#</a> 主要方法</h4> <div class="language- line-numbers-mode"><pre class="language-text"><code>// 得到给定时间戳的值，如果不存在返回 null（要求传入的 timestamp 是递增的） |
| Object getValueInTimestamp(long timestamp) throws IOException; |
| |
| // 给定一批递增时间戳的值，返回一批结果（减少方法调用次数） |
| Object[] getValuesInTimestamps(long[] timestamps) throws IOException; |
| </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></div></div><h4 id="一般使用流程-2"><a href="#一般使用流程-2" class="header-anchor">#</a> 一般使用流程</h4> <p>该接口在带值过滤的查询中被使用，TimeGenerator生成时间戳后，使用该接口获得该时间戳对应的value</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>Object value = readerByTimestamp.getValueInTimestamp(timestamp); |
| |
| or |
| |
| Object[] values = readerByTimestamp.getValueInTimestamp(timestamps); |
| </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></div></div><h2 id="具体实现类"><a href="#具体实现类" class="header-anchor">#</a> 具体实现类</h2> <p>上述三个接口都有其对应的实现类，由于以上三种查询有共性，我们设计了一个基础的 SeriesReader 工具类，封装了对于一个时间序列读取操作的基本方法，帮助实现以上三种接口。下面首先介绍 SeriesReader 的设计原理，然后再依次介绍三个接口的具体实现。</p> <h3 id="org-apache-iotdb-db-query-reader-series-seriesreader"><a href="#org-apache-iotdb-db-query-reader-series-seriesreader" class="header-anchor">#</a> org.apache.iotdb.db.query.reader.series.SeriesReader</h3> <h4 id="设计思想"><a href="#设计思想" class="header-anchor">#</a> 设计思想</h4> <p>背景知识：TsFile 文件（TsFileResource）解开后可以得到 ChunkMetadata，ChunkMetadata 解开后可以得到一堆 PageReader，PageReader 可以直接返回 BatchData 数据点。</p> <p>为了支持以上三种接口</p> <p>数据按照粒度从大到小分成四种：文件，Chunk，Page，相交数据点。在原始数据查询中，最大的数据块返回粒度是一个 page，如果一个 page 和其他 page 由于乱序写入相互覆盖了，就解开成数据点做合并。聚合查询中优先使用 Chunk 的统计信息，其次是 Page 的统计信息，最后是相交数据点。</p> <p>设计原则是能用粒度大的就不用粒度小的。</p> <p>首先介绍一下SeriesReader里的几个重要字段</p> <div class="language- line-numbers-mode"><pre class="language-text"><code> |
| /* |
| * 文件层 |
| */ |
| private final List<TsFileResource> seqFileResource; |
| 顺序文件列表，因为顺序文件本身就保证有序，且时间戳互不重叠，只需使用List进行存储 |
| |
| private final PriorityQueue<TsFileResource> unseqFileResource; |
| 乱序文件列表，因为乱序文件互相之间不保证顺序性，且可能有重叠，为了保证顺序，使用优先队列进行存储 |
| |
| /* |
| * chunk 层 |
| * |
| * 三个字段之间数据永远不重复，first 永远是第一个（开始时间最小） |
| */ |
| private ChunkMetaData firstChunkMetaData; |
| 填充 chunk 层时优先填充此字段，保证这个 chunk 具有当前最小开始时间 |
| |
| private final List<ChunkMetaData> seqChunkMetadatas; |
| 顺序文件解开后得到的 ChunkMetaData 存放在此，本身有序且互不重叠，所以使用 List 存储 |
| |
| private final PriorityQueue<ChunkMetaData> unseqChunkMetadatas; |
| 乱序文件解开后得到的 ChunkMetaData 存放在此，互相之间可能有重叠，为了保证顺序，使用优先队列进行存储 |
| |
| /* |
| * page 层 |
| * |
| * 两个字段之间数据永远不重复，first 永远是第一个（开始时间最小） |
| */ |
| private VersionPageReader firstPageReader; |
| 开始时间最小的 page reader |
| |
| private PriorityQueue<VersionPageReader> cachedPageReaders; |
| 当前获得的所有 page reader，按照每个 page 的起始时间进行排序 |
| |
| /* |
| * 相交数据点层 |
| */ |
| private PriorityMergeReader mergeReader; |
| 本质上是多个带优先级的 page，按时间戳从低到高输出数据点，时间戳相同时，保留优先级高的 |
| |
| /* |
| * 相交数据点产出结果的缓存 |
| */ |
| private boolean hasCachedNextOverlappedPage; |
| 是否缓存了下一个batch |
| |
| private BatchData cachedBatchData; |
| 缓存的下一个batch的引用 |
| </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><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br><span class="line-number">49</span><br></div></div><p>下面介绍一下SeriesReader里的重要方法</p> <h4 id="hasnextchunk"><a href="#hasnextchunk" class="header-anchor">#</a> hasNextChunk()</h4> <ul><li><p>主要功能：判断该时间序列还有没有下一个chunk。</p></li> <li><p>约束：在调用这个方法前，需要保证 <code>SeriesReader</code> 内已经没有 page 和 数据点 层级的数据了，也就是之前解开的 chunk 都消耗完了。</p></li> <li><p>实现：如果 <code>firstChunkMetaData</code> 不为空，则代表当前已经缓存了第一个 <code>ChunkMetaData</code>，且未被使用，直接返回<code>true</code>；</p> <p>尝试去解开第一个顺序文件和第一个乱序文件，填充 chunk 层。并解开与 <code>firstChunkMetadata</code> 相重合的所有文件。</p></li></ul> <h4 id="ischunkoverlapped"><a href="#ischunkoverlapped" class="header-anchor">#</a> isChunkOverlapped()</h4> <ul><li><p>主要功能：判断当前的 chunk 有没有与其他 Chunk 有重叠</p></li> <li><p>约束：在调用这个方法前，需要保证 chunk 层已经缓存了 <code>firstChunkMetadata</code>，也就是调用了 hasNextChunk() 并且为 true。</p></li> <li><p>实现：直接把 <code>firstChunkMetadata</code> 与 <code>seqChunkMetadatas</code> 和 <code>unseqChunkMetadatas</code> 相比较。因为此前已经保证所有和 <code>firstChunkMetadata</code> 相交的文件都被解开了。</p></li></ul> <h4 id="currentchunkstatistics"><a href="#currentchunkstatistics" class="header-anchor">#</a> currentChunkStatistics()</h4> <p>返回 <code>firstChunkMetaData</code> 的统计信息。</p> <h4 id="skipcurrentchunk"><a href="#skipcurrentchunk" class="header-anchor">#</a> skipCurrentChunk()</h4> <p>跳过当前 chunk。只需要将<code>firstChunkMetaData</code>置为<code>null</code>。</p> <h4 id="hasnextpage"><a href="#hasnextpage" class="header-anchor">#</a> hasNextPage()</h4> <ul><li><p>主要功能：判断 SeriesReader 中还有没有已经解开的 page，如果有相交的 page，就构造 <code>cachedBatchData</code> 并缓存，否则缓存 <code>firstPageReader</code>。</p></li> <li><p>实现：如果已经缓存了 <code>cachedBatchData</code> 就直接返回。如果有相交数据点，就构造 <code>cachedBatchData</code>。如果已经缓存了 <code>firstPageReader</code>，就直接返回。</p> <p>如果当前的 <code>firstChunkMetadata</code> 还没有解开，就解开与之重叠的所有 ChunkMetadata，构造 firstPageReader。</p> <p>判断，如果 <code>firstPageReader</code> 和 <code>cachedPageReaders</code> 相交，则构造 <code>cachedBatchData</code>，否则直接返回。</p></li></ul> <h4 id="ispageoverlapped"><a href="#ispageoverlapped" class="header-anchor">#</a> isPageOverlapped()</h4> <ul><li><p>主要功能：判断当前的 page 有没有与其他 page 有重叠</p></li> <li><p>约束：在调用这个方法前，需要保证调用了 hasNextPage() 并且为 true。也就是，有可能缓存了一个相交的 <code>cachedBatchData</code>，或者缓存了不相交的 <code>firstPageReader</code>。</p></li> <li><p>实现：先判断有没有 <code>cachedBatchData</code>，如果没有，就说明当前 page 不相交，则 <code>mergeReader</code> 里没数据。再判断 <code>firstPageReader</code> 是否与 <code>cachedPageReaders</code> 中的 page 相交。</p></li></ul> <h4 id="currentpagestatistics"><a href="#currentpagestatistics" class="header-anchor">#</a> currentPageStatistics()</h4> <p>返回 <code>firstPageReader</code> 的统计信息。</p> <h4 id="skipcurrentpage"><a href="#skipcurrentpage" class="header-anchor">#</a> skipCurrentPage()</h4> <p>跳过当前Page。只需要将 <code>firstPageReader</code> 置为 null。</p> <h4 id="nextpage"><a href="#nextpage" class="header-anchor">#</a> nextPage()</h4> <ul><li><p>主要功能：返回下一个相交或不相交的 page</p></li> <li><p>约束：在调用这个方法前，需要保证调用了 hasNextPage() 并且为 true。也就是，有可能缓存了一个相交的 <code>cachedBatchData</code>，或者缓存了不相交的 <code>firstPageReader</code>。</p></li> <li><p>实现：如果 <code>hasCachedNextOverlappedPage</code> 为 true，说明缓存了一个相交的 page，直接返回 <code>cachedBatchData</code>。否则当前 page 不相交，直接从 firstPageReader 里拿当前 page 的数据。</p></li></ul> <h4 id="hasnextoverlappedpage"><a href="#hasnextoverlappedpage" class="header-anchor">#</a> hasNextOverlappedPage()</h4> <ul><li><p>主要功能：内部方法，用来判断当前有没有重叠的数据，并且构造相交的 page 并缓存。</p></li> <li><p>实现：如果 <code>hasCachedNextOverlappedPage</code> 为 <code>true</code>，直接返回 <code>true</code>。</p> <p>否则，先调用 <code>tryToPutAllDirectlyOverlappedPageReadersIntoMergeReader()</code> 方法，将 <code>cachedPageReaders</code> 中所有与 <code>firstPageReader</code> 有重叠的放进 <code>mergeReader</code> 里。<code>mergeReader</code> 里维护了一个 <code>currentLargestEndTime</code> 变量，每次添加进新的 Reader 时被更新，用以记录当前添加进 <code>mergeReader</code> 的 page 的最大结束时间。 |
| 然后先从<code>mergeReader</code>里取出当前最大的结束时间，作为第一批数据的结束时间，记为<code>currentPageEndTime</code>。接着去遍历<code>mergeReader</code>，直到当前的时间戳大于<code>currentPageEndTime</code>。</p> <p>每从 mergeReader 移出一个点前，我们先要判断是否有与当前时间戳重叠的file或者chunk或者page（这里之所以还要再做一次判断，是因为，比如当前page是1-30，和他直接相交的page是20-50，还有一个page是40-60，每取一个点判断一次是想把40-60解开），如果有，解开相应的file或者chunk或者page，并将其放入<code>mergeReader</code>。完成重叠的判断后，从<code>mergeReader</code>中取出相应数据。</p> <p>完成迭代后将获得数据缓存在 <code>cachedBatchData</code> 中，并将 <code>hasCachedNextOverlappedPage</code> 置为 <code>true</code>。</p></li></ul> <h4 id="nextoverlappedpage"><a href="#nextoverlappedpage" class="header-anchor">#</a> nextOverlappedPage()</h4> <p>将缓存的<code>cachedBatchData</code>返回，并将<code>hasCachedNextOverlappedPage</code>置为<code>false</code>。</p> <h3 id="org-apache-iotdb-db-query-reader-series-seriesrawdatabatchreader"><a href="#org-apache-iotdb-db-query-reader-series-seriesrawdatabatchreader" class="header-anchor">#</a> org.apache.iotdb.db.query.reader.series.SeriesRawDataBatchReader</h3> <p><code>SeriesRawDataBatchReader</code>实现了<code>IBatchReader</code>。</p> <p>其方法<code>hasNextBatch()</code>的核心判断流程是</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>// 有缓存了 batch，直接返回 |
| if (hasCachedBatchData) { |
| return true; |
| } |
| |
| /* |
| * 如果 SeriesReader 里还有 page，返回 page |
| */ |
| if (readPageData()) { |
| hasCachedBatchData = true; |
| return true; |
| } |
| |
| /* |
| * 如果有 chunk，并且有 page，返回 page |
| */ |
| while (seriesReader.hasNextChunk()) { |
| if (readPageData()) { |
| hasCachedBatchData = true; |
| return true; |
| } |
| } |
| return hasCachedBatchData; |
| </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></div></div><h3 id="org-apache-iotdb-db-query-reader-series-seriesreaderbytimestamp"><a href="#org-apache-iotdb-db-query-reader-series-seriesreaderbytimestamp" class="header-anchor">#</a> org.apache.iotdb.db.query.reader.series.SeriesReaderByTimestamp</h3> <p><code>SeriesReaderByTimestamp</code> 实现了 <code>IReaderByTimestamp</code>。</p> <p>设计思想：当给一个时间戳要查询值时，这个时间戳可以转化为一个 time >= x 的过滤条件。不断更新这个过滤条件，并且跳过不满足的文件，chunk 和 page。</p> <p>实现方式：</p> <div class="language- line-numbers-mode"><pre class="language-text"><code>/* |
| * 优先判断下一个 page 有没有当前所查时间，能跳过就跳过 |
| */ |
| if (readPageData(timestamp)) { |
| return true; |
| } |
| |
| /* |
| * 判断下一个 chunk 有没有当前所查时间，能跳过就跳过 |
| */ |
| while (seriesReader.hasNextChunk()) { |
| Statistics statistics = seriesReader.currentChunkStatistics(); |
| if (!satisfyTimeFilter(statistics)) { |
| seriesReader.skipCurrentChunk(); |
| continue; |
| } |
| /* |
| * chunk 不能跳过，继续到 chunk 里检查 page |
| */ |
| if (readPageData(timestamp)) { |
| return true; |
| } |
| } |
| return false; |
| </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></div></div><h3 id="org-apache-iotdb-db-query-reader-series-seriesaggregatereader"><a href="#org-apache-iotdb-db-query-reader-series-seriesaggregatereader" class="header-anchor">#</a> org.apache.iotdb.db.query.reader.series.SeriesAggregateReader</h3> <p><code>SeriesAggregateReader</code> 实现了 <code>IAggregateReader</code></p> <p><code>IAggregateReader</code>的大部分接口方法都在<code>SeriesReader</code>有对应实现，除了<code>canUseCurrentChunkStatistics()</code>和<code>canUseCurrentPageStatistics()</code>两个方法。</p> <h4 id="canusecurrentchunkstatistics"><a href="#canusecurrentchunkstatistics" class="header-anchor">#</a> canUseCurrentChunkStatistics()</h4> <p>设计思想：可以用统计信息的条件是当前 chunk 不重叠，并且满足过滤条件。</p> <p>先调用<code>SeriesReader</code>的<code>currentChunkStatistics()</code>方法，获得当前chunk的统计信息，再调用<code>SeriesReader</code>的<code>isChunkOverlapped()</code>方法判断当前chunk是否重叠，如果当前chunk不重叠，且其统计信息满足过滤条件，则返回<code>true</code>，否则返回<code>false</code>。</p> <h4 id="canusecurrentpagestatistics"><a href="#canusecurrentpagestatistics" class="header-anchor">#</a> canUseCurrentPageStatistics()</h4> <p>设计思想：可以用统计信息的条件是当前 page 不重叠，并且满足过滤条件。</p> <p>先调用<code>SeriesReader</code>的 <code>currentPageStatistics()</code> 方法，获得当前page的统计信息，再调用<code>SeriesReader</code> 的 <code>isPageOverlapped()</code> 方法判断当前 page 是否重叠，如果当前page不重叠，且其统计信息满足过滤条件，则返回<code>true</code>，否则返回<code>false</code>。</p></div> <div class="page-nav"><p class="inner"><span class="prev"> |
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