mirror of https://github.com/apache/druid.git
82 lines
2.5 KiB
Markdown
82 lines
2.5 KiB
Markdown
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---
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layout: doc_page
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---
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# Segment Metadata Queries
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Segment metadata queries return per segment information about:
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* Cardinality of all columns in the segment
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* Estimated byte size for the segment columns if they were stored in a flat format
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* Interval the segment covers
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* Column type of all the columns in the segment
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* Estimated total segment byte size in if it was stored in a flat format
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* Segment id
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```json
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{
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"queryType":"segmentMetadata",
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"dataSource":"sample_datasource",
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"intervals":["2013-01-01/2014-01-01"]
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}
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```
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There are several main parts to a segment metadata query:
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|property|description|required?|
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|--------|-----------|---------|
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|queryType|This String should always be "segmentMetadata"; this is the first thing Druid looks at to figure out how to interpret the query|yes|
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|dataSource|A String or Object defining the data source to query, very similar to a table in a relational database. See [DataSource](../querying/datasource.html) for more information.|yes|
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|intervals|A JSON Object representing ISO-8601 Intervals. This defines the time ranges to run the query over.|yes|
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|toInclude|A JSON Object representing what columns should be included in the result. Defaults to "all".|no|
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|merge|Merge all individual segment metadata results into a single result|no|
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|context|See [Context](../querying/query-context.html)|no|
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The format of the result is:
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```json
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[ {
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"id" : "some_id",
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"intervals" : [ "2013-05-13T00:00:00.000Z/2013-05-14T00:00:00.000Z" ],
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"columns" : {
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"__time" : { "type" : "LONG", "size" : 407240380, "cardinality" : null },
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"dim1" : { "type" : "STRING", "size" : 100000, "cardinality" : 1944 },
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"dim2" : { "type" : "STRING", "size" : 100000, "cardinality" : 1504 },
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"metric1" : { "type" : "FLOAT", "size" : 100000, "cardinality" : null }
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},
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"size" : 300000
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} ]
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```
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Dimension columns will have type `STRING`.
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Metric columns will have type `FLOAT` or `LONG` or name of the underlying complex type such as `hyperUnique` in case of COMPLEX metric.
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Timestamp column will have type `LONG`.
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Only columns which are dimensions (ie, have type `STRING`) will have any cardinality. Rest of the columns (timestamp and metric columns) will show cardinality as `null`.
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### toInclude
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There are 3 types of toInclude objects.
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#### All
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The grammar is as follows:
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``` json
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"toInclude": { "type": "all"}
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```
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#### None
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The grammar is as follows:
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``` json
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"toInclude": { "type": "none"}
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```
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#### List
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The grammar is as follows:
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``` json
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"toInclude": { "type": "list", "columns": [<string list of column names>]}
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```
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