Stream from Unity Catalog views

In Databricks Runtime 14.1 and above, you can use Structured Streaming to perform streaming reads from views registered with Unity Catalog. Azure Databricks only supports streaming reads from views defined against Delta tables.

Read a view as a stream

To read a view with Structured Streaming, provide the identifier for the view to the .table() method, as in the following example:

df = (spark.readStream
  .table("demoView")
)

Users must have SELECT privileges on the target view.

Supported options for configuring streaming reads against views

The following options are supported when configuring streaming reads against views:

• maxFilesPerTrigger
• maxBytesPerTrigger
• ignoreDeletes
• skipChangeCommits
• withEventTimeOrder
• startingTimestamp
• startingVersion

The streaming reader applies these options to the files and metadata defining the underlying Delta tables.

Supported operations in source views

Not all views support streaming reads. Unsupported operations in source views include aggregations and sorting.

The following list provides descriptions and example view definitions for supported operations:

• Project

  • Description: Controls column-level permissions

  • Operator: SELECT... FROM...

  • Example statement:

    CREATE VIEW project_view AS
    SELECT id, value
    FROM source_table
    

• Filter

  • Description: Controls row-level permissions

  • Operator: WHERE...

  • Example statement:

    CREATE VIEW filter_view AS
    SELECT * FROM source_table
    WHERE value > 100
    

• Union all

  • Description: Results from multiple tables

  • Operator: UNION ALL

  • Example statement:

    CREATE VIEW union_view AS
    SELECT id, value FROM source_table1
    UNION ALL
    SELECT * FROM source_table2
    

Limitations

The following limitations apply:

• You can only stream from views backed by Delta tables. Views defined against other data sources are not supported.

• You must register views with Unity Catalog.

• The following exception displays if you stream from a view with an unsupported operator:

  UnsupportedOperationException: [UNEXPECTED_OPERATOR_IN_STREAMING_VIEW] Unexpected operator <operator> in the CREATE VIEW statement as a streaming source. A streaming view query must consist only of SELECT, WHERE, and UNION ALL operations.
  

• The following exception displays if you provide unsupported options:

  AnalysisException: [UNSUPPORTED_STREAMING_OPTIONS_FOR_VIEW.UNSUPPORTED_OPTION] Unsupported for streaming a view. Reason: option <option> is not supported.