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| |
| <h1 id="segment-metadata-queries">Segment Metadata Queries</h1> |
| |
| <p>Segment metadata queries return per-segment information about:</p> |
| |
| <ul> |
| <li>Cardinality of all columns in the segment</li> |
| <li>Min/max values of string type columns in the segment</li> |
| <li>Estimated byte size for the segment columns if they were stored in a flat format</li> |
| <li>Number of rows stored inside the segment</li> |
| <li>Interval the segment covers</li> |
| <li>Column type of all the columns in the segment</li> |
| <li>Estimated total segment byte size in if it was stored in a flat format</li> |
| <li>Is the segment rolled up</li> |
| <li>Segment id</li> |
| </ul> |
| <div class="highlight"><pre><code class="language-json" data-lang="json"><span></span><span class="p">{</span> |
| <span class="nt">"queryType"</span><span class="p">:</span><span class="s2">"segmentMetadata"</span><span class="p">,</span> |
| <span class="nt">"dataSource"</span><span class="p">:</span><span class="s2">"sample_datasource"</span><span class="p">,</span> |
| <span class="nt">"intervals"</span><span class="p">:[</span><span class="s2">"2013-01-01/2014-01-01"</span><span class="p">]</span> |
| <span class="p">}</span> |
| </code></pre></div> |
| <p>There are several main parts to a segment metadata query:</p> |
| |
| <table><thead> |
| <tr> |
| <th>property</th> |
| <th>description</th> |
| <th>required?</th> |
| </tr> |
| </thead><tbody> |
| <tr> |
| <td>queryType</td> |
| <td>This String should always be "segmentMetadata"; this is the first thing Apache Druid (incubating) looks at to figure out how to interpret the query</td> |
| <td>yes</td> |
| </tr> |
| <tr> |
| <td>dataSource</td> |
| <td>A String or Object defining the data source to query, very similar to a table in a relational database. See <a href="../querying/datasource.html">DataSource</a> for more information.</td> |
| <td>yes</td> |
| </tr> |
| <tr> |
| <td>intervals</td> |
| <td>A JSON Object representing ISO-8601 Intervals. This defines the time ranges to run the query over.</td> |
| <td>no</td> |
| </tr> |
| <tr> |
| <td>toInclude</td> |
| <td>A JSON Object representing what columns should be included in the result. Defaults to "all".</td> |
| <td>no</td> |
| </tr> |
| <tr> |
| <td>merge</td> |
| <td>Merge all individual segment metadata results into a single result</td> |
| <td>no</td> |
| </tr> |
| <tr> |
| <td>context</td> |
| <td>See <a href="../querying/query-context.html">Context</a></td> |
| <td>no</td> |
| </tr> |
| <tr> |
| <td>analysisTypes</td> |
| <td>A list of Strings specifying what column properties (e.g. cardinality, size) should be calculated and returned in the result. Defaults to ["cardinality", "interval", "minmax"], but can be overridden with using the <a href="../configuration/index.html#segment-metadata-query-config">segment metadata query config</a>. See section <a href="#analysistypes">analysisTypes</a> for more details.</td> |
| <td>no</td> |
| </tr> |
| <tr> |
| <td>lenientAggregatorMerge</td> |
| <td>If true, and if the "aggregators" analysisType is enabled, aggregators will be merged leniently. See below for details.</td> |
| <td>no</td> |
| </tr> |
| </tbody></table> |
| |
| <p>The format of the result is:</p> |
| <div class="highlight"><pre><code class="language-json" data-lang="json"><span></span><span class="p">[</span> <span class="p">{</span> |
| <span class="nt">"id"</span> <span class="p">:</span> <span class="s2">"some_id"</span><span class="p">,</span> |
| <span class="nt">"intervals"</span> <span class="p">:</span> <span class="p">[</span> <span class="s2">"2013-05-13T00:00:00.000Z/2013-05-14T00:00:00.000Z"</span> <span class="p">],</span> |
| <span class="nt">"columns"</span> <span class="p">:</span> <span class="p">{</span> |
| <span class="nt">"__time"</span> <span class="p">:</span> <span class="p">{</span> <span class="nt">"type"</span> <span class="p">:</span> <span class="s2">"LONG"</span><span class="p">,</span> <span class="nt">"hasMultipleValues"</span> <span class="p">:</span> <span class="kc">false</span><span class="p">,</span> <span class="nt">"size"</span> <span class="p">:</span> <span class="mi">407240380</span><span class="p">,</span> <span class="nt">"cardinality"</span> <span class="p">:</span> <span class="kc">null</span><span class="p">,</span> <span class="nt">"errorMessage"</span> <span class="p">:</span> <span class="kc">null</span> <span class="p">},</span> |
| <span class="nt">"dim1"</span> <span class="p">:</span> <span class="p">{</span> <span class="nt">"type"</span> <span class="p">:</span> <span class="s2">"STRING"</span><span class="p">,</span> <span class="nt">"hasMultipleValues"</span> <span class="p">:</span> <span class="kc">false</span><span class="p">,</span> <span class="nt">"size"</span> <span class="p">:</span> <span class="mi">100000</span><span class="p">,</span> <span class="nt">"cardinality"</span> <span class="p">:</span> <span class="mi">1944</span><span class="p">,</span> <span class="nt">"errorMessage"</span> <span class="p">:</span> <span class="kc">null</span> <span class="p">},</span> |
| <span class="nt">"dim2"</span> <span class="p">:</span> <span class="p">{</span> <span class="nt">"type"</span> <span class="p">:</span> <span class="s2">"STRING"</span><span class="p">,</span> <span class="nt">"hasMultipleValues"</span> <span class="p">:</span> <span class="kc">true</span><span class="p">,</span> <span class="nt">"size"</span> <span class="p">:</span> <span class="mi">100000</span><span class="p">,</span> <span class="nt">"cardinality"</span> <span class="p">:</span> <span class="mi">1504</span><span class="p">,</span> <span class="nt">"errorMessage"</span> <span class="p">:</span> <span class="kc">null</span> <span class="p">},</span> |
| <span class="nt">"metric1"</span> <span class="p">:</span> <span class="p">{</span> <span class="nt">"type"</span> <span class="p">:</span> <span class="s2">"FLOAT"</span><span class="p">,</span> <span class="nt">"hasMultipleValues"</span> <span class="p">:</span> <span class="kc">false</span><span class="p">,</span> <span class="nt">"size"</span> <span class="p">:</span> <span class="mi">100000</span><span class="p">,</span> <span class="nt">"cardinality"</span> <span class="p">:</span> <span class="kc">null</span><span class="p">,</span> <span class="nt">"errorMessage"</span> <span class="p">:</span> <span class="kc">null</span> <span class="p">}</span> |
| <span class="p">},</span> |
| <span class="nt">"aggregators"</span> <span class="p">:</span> <span class="p">{</span> |
| <span class="nt">"metric1"</span> <span class="p">:</span> <span class="p">{</span> <span class="nt">"type"</span> <span class="p">:</span> <span class="s2">"longSum"</span><span class="p">,</span> <span class="nt">"name"</span> <span class="p">:</span> <span class="s2">"metric1"</span><span class="p">,</span> <span class="nt">"fieldName"</span> <span class="p">:</span> <span class="s2">"metric1"</span> <span class="p">}</span> |
| <span class="p">},</span> |
| <span class="nt">"queryGranularity"</span> <span class="p">:</span> <span class="p">{</span> |
| <span class="nt">"type"</span><span class="p">:</span> <span class="s2">"none"</span> |
| <span class="p">},</span> |
| <span class="nt">"size"</span> <span class="p">:</span> <span class="mi">300000</span><span class="p">,</span> |
| <span class="nt">"numRows"</span> <span class="p">:</span> <span class="mi">5000000</span> |
| <span class="p">}</span> <span class="p">]</span> |
| </code></pre></div> |
| <p>Dimension columns will have type <code>STRING</code>. |
| Metric columns will have type <code>FLOAT</code> or <code>LONG</code> or name of the underlying complex type such as <code>hyperUnique</code> in case of COMPLEX metric. |
| Timestamp column will have type <code>LONG</code>.</p> |
| |
| <p>If the <code>errorMessage</code> field is non-null, you should not trust the other fields in the response. Their contents are |
| undefined.</p> |
| |
| <p>Only columns which are dimensions (ie, have type <code>STRING</code>) will have any cardinality. Rest of the columns (timestamp and metric columns) will show cardinality as <code>null</code>.</p> |
| |
| <h3 id="intervals">intervals</h3> |
| |
| <p>If an interval is not specified, the query will use a default interval that spans a configurable period before the end time of the most recent segment.</p> |
| |
| <p>The length of this default time period is set in the Broker configuration via: |
| druid.query.segmentMetadata.defaultHistory</p> |
| |
| <h3 id="toinclude">toInclude</h3> |
| |
| <p>There are 3 types of toInclude objects.</p> |
| |
| <h4 id="all">All</h4> |
| |
| <p>The grammar is as follows:</p> |
| <div class="highlight"><pre><code class="language-json" data-lang="json"><span></span><span class="s2">"toInclude"</span><span class="err">:</span> <span class="p">{</span> <span class="nt">"type"</span><span class="p">:</span> <span class="s2">"all"</span><span class="p">}</span> |
| </code></pre></div> |
| <h4 id="none">None</h4> |
| |
| <p>The grammar is as follows:</p> |
| <div class="highlight"><pre><code class="language-json" data-lang="json"><span></span><span class="s2">"toInclude"</span><span class="err">:</span> <span class="p">{</span> <span class="nt">"type"</span><span class="p">:</span> <span class="s2">"none"</span><span class="p">}</span> |
| </code></pre></div> |
| <h4 id="list">List</h4> |
| |
| <p>The grammar is as follows:</p> |
| <div class="highlight"><pre><code class="language-json" data-lang="json"><span></span><span class="s2">"toInclude"</span><span class="err">:</span> <span class="p">{</span> <span class="nt">"type"</span><span class="p">:</span> <span class="s2">"list"</span><span class="p">,</span> <span class="nt">"columns"</span><span class="p">:</span> <span class="p">[</span><span class="err"><string</span> <span class="err">list</span> <span class="err">of</span> <span class="err">column</span> <span class="err">names></span><span class="p">]}</span> |
| </code></pre></div> |
| <h3 id="analysistypes">analysisTypes</h3> |
| |
| <p>This is a list of properties that determines the amount of information returned about the columns, i.e. analyses to be performed on the columns.</p> |
| |
| <p>By default, the "cardinality", "interval", and "minmax" types will be used. If a property is not needed, omitting it from this list will result in a more efficient query.</p> |
| |
| <p>The default analysis types can be set in the Broker configuration via: |
| <code>druid.query.segmentMetadata.defaultAnalysisTypes</code></p> |
| |
| <p>Types of column analyses are described below:</p> |
| |
| <h4 id="cardinality">cardinality</h4> |
| |
| <ul> |
| <li><code>cardinality</code> in the result will return the estimated floor of cardinality for each column. Only relevant for |
| dimension columns.</li> |
| </ul> |
| |
| <h4 id="minmax">minmax</h4> |
| |
| <ul> |
| <li>Estimated min/max values for each column. Only relevant for dimension columns.</li> |
| </ul> |
| |
| <h4 id="size">size</h4> |
| |
| <ul> |
| <li><code>size</code> in the result will contain the estimated total segment byte size as if the data were stored in text format</li> |
| </ul> |
| |
| <h4 id="interval">interval</h4> |
| |
| <ul> |
| <li><code>intervals</code> in the result will contain the list of intervals associated with the queried segments.</li> |
| </ul> |
| |
| <h4 id="timestampspec">timestampSpec</h4> |
| |
| <ul> |
| <li><code>timestampSpec</code> in the result will contain timestampSpec of data stored in segments. this can be null if timestampSpec of segments was unknown or unmergeable (if merging is enabled).</li> |
| </ul> |
| |
| <h4 id="querygranularity">queryGranularity</h4> |
| |
| <ul> |
| <li><code>queryGranularity</code> in the result will contain query granularity of data stored in segments. this can be null if query granularity of segments was unknown or unmergeable (if merging is enabled).</li> |
| </ul> |
| |
| <h4 id="aggregators">aggregators</h4> |
| |
| <ul> |
| <li><p><code>aggregators</code> in the result will contain the list of aggregators usable for querying metric columns. This may be |
| null if the aggregators are unknown or unmergeable (if merging is enabled).</p></li> |
| <li><p>Merging can be strict or lenient. See <em>lenientAggregatorMerge</em> below for details.</p></li> |
| <li><p>The form of the result is a map of column name to aggregator.</p></li> |
| </ul> |
| |
| <h4 id="rollup">rollup</h4> |
| |
| <ul> |
| <li><code>rollup</code> in the result is true/false/null.</li> |
| <li>When merging is enabled, if some are rollup, others are not, result is null.</li> |
| </ul> |
| |
| <h3 id="lenientaggregatormerge">lenientAggregatorMerge</h3> |
| |
| <p>Conflicts between aggregator metadata across segments can occur if some segments have unknown aggregators, or if |
| two segments use incompatible aggregators for the same column (e.g. longSum changed to doubleSum).</p> |
| |
| <p>Aggregators can be merged strictly (the default) or leniently. With strict merging, if there are any segments |
| with unknown aggregators, or any conflicts of any kind, the merged aggregators list will be <code>null</code>. With lenient |
| merging, segments with unknown aggregators will be ignored, and conflicts between aggregators will only null out |
| the aggregator for that particular column.</p> |
| |
| <p>In particular, with lenient merging, it is possible for an invidiual column's aggregator to be <code>null</code>. This will not |
| occur with strict merging.</p> |
| |
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