Extent tags

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Applies to: ✅ Azure Data Explorer

An extent tag is a string that describes properties common to all data in an extent. For example, during data ingestion, you can append an extent tag to signify the source of the ingested data. Then, you can use this tag for analysis.

Extents can hold multiple tags as part of their metadata. When extents merge, their tags also merge, ensuring consistent metadata representation.

To see the tags associated with an extent, use the .show extents command. For a granular view of tags associated with records within an extent, use the extent-tags() function.

Important

Tags starting with drop-by: or ingest-by: carry specific meanings. For more information, see drop-by extent tags and ingest-by extent tags.

drop-by extent tags

Tags that start with a drop-by: prefix can be used to control which other extents to merge with. Extents that have the same set of drop-by: tags can be merged together, but they won't be merged with other extents if they have a different set of drop-by: tags.

Note

  • Avoid excessive use of drop-by tags.
  • These tags shouldn't be used to replace individual record-level data, and they are most effective when applied to large amounts of data.
  • Assigning unique drop-by tags to individual records or files can significantly impact performance.

Examples

Determine which extents can be merged together

If:

  • Extent 1 has the following tags: drop-by:blue, drop-by:red, green.
  • Extent 2 has the following tags: drop-by:red, yellow.
  • Extent 3 has the following tags: purple, drop-by:red, drop-by:blue.

Then:

  • Extents 1 and 2 won't be merged together, as they have a different set of drop-by tags.
  • Extents 2 and 3 won't be merged together, as they have a different set of drop-by tags.
  • Extents 1 and 3 can be merged together, as they have the same set of drop-by tags.

Use drop-by tags as part of extent-level operations

The following query issues a command to drop extents according to their drop-by: tag.

.ingest ... with @'{"tags":"[\"drop-by:2016-02-17\"]"}'

.drop extents <| .show table MyTable extents where tags has "drop-by:2016-02-17"

ingest-by extent tags

Tags with the prefix ingest-by: can be used together with the ingestIfNotExists property to ensure that data is ingested only once.

The ingestIfNotExists property prevents duplicate ingestion by checking if an extent with the specified ingest-by: tag already exists. Typically, an ingest command contains an ingest-by: tag and the ingestIfNotExists property with the same value.

Note

  • Avoid excessive use of ingest-by tags.
  • Assigning unique ingest-by tags for each ingestion call can significantly impact performance.
  • If the pipeline is known to have data duplications, we recommend that you solve these duplications before ingesting data.

Examples

Add a tag on ingestion

The following command ingests the data and adds the tag ingest-by:2016-02-17.

.ingest ... with (tags = '["ingest-by:2016-02-17"]')

Prevent duplicate ingestion

The following command ingests the data so long as no extent in the table has the ingest-by:2016-02-17 tag.

.ingest ... with (ingestIfNotExists = '["2016-02-17"]')

Prevent duplicate ingestion and add a tag to any new data

The following command ingests the data so long as no extent in the table has the ingest-by:2016-02-17 tag. Any newly ingested data gets the ingest-by:2016-02-17 tag.

.ingest ... with (ingestIfNotExists = '["2016-02-17"]', tags = '["ingest-by:2016-02-17"]')

Limitations

  • Extent tags can only be applied to records within an extent. Consequently, tags can't be set on streaming ingestion data before it is stored in extents.
  • Extent tags can't be stored on data in external tables or materialized views.

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