Daily DAX : Day 211 INFO.GENERALSEGMENTMAPSEGMENTMETADATASTORAGES

 The INFO.GENERALSEGMENTMAPSEGMENTMETADATASTORAGES DAX function in Power BI is one of the INFO functions introduced to provide metadata about the underlying data model. Specifically, this function returns a table containing information about the segment map segment metadata storages in the current Power BI semantic model. These storages are related to how data is segmented and managed within the model's storage engine, particularly in the context of Analysis Services' tabular engine.

Syntax

INFO.GENERALSEGMENTMAPSEGMENTMETADATASTORAGES()

    No parameters: This function does not take any arguments.

    Return value: A table with columns that match the schema rowset for segment map segment metadata storage objects, providing details about how segments are stored and managed in the model.

Key Characteristics

    Output: The function outputs a table data type, which can be used with other DAX functions like FILTER, SELECTCOLUMNS, or ADDCOLUMNS for further manipulation.

    Restrictions: 

        It cannot be used in calculated columns or calculated tables; it is designed for use in DAX queries, typically within DAX Query View in Power BI Desktop.

        It requires semantic model admin permissions to access the metadata, similar to other INFO functions.

    Context: This function is part of the broader set of INFO functions that mirror the Dynamic Management Views (DMVs) in Analysis Services, adapted to work as native DAX functions.

    Compatibility: The function is supported in Power BI semantic models but not in SQL Server Analysis Services, Azure Analysis Services, or PowerPivot models.

Columns in the Output Table

The exact schema of the table returned by INFO.GENERALSEGMENTMAPSEGMENTMETADATASTORAGES is not fully documented in public Microsoft documentation, as noted in the DAX Guide. However, based on its purpose, the table likely includes columns such as:

    Identifiers for segment map storage objects.

    Metadata about segment size, location, or configuration.

    Information about how data is partitioned or stored within the model's storage engine.

Since Microsoft documentation for this specific function is limited or unsupported, the exact column names and their meanings may require exploration using tools like DAX Studio or DAX Query View to inspect the output.

Use Case

The INFO.GENERALSEGMENTMAPSEGMENTMETADATASTORAGES function is primarily used for model optimization and debugging by advanced Power BI developers or administrators. Its key use cases include:

    Model Performance Analysis:

        Understanding how data segments are stored can help identify inefficiencies in the storage engine, such as overly large segments or suboptimal partitioning.

        This is particularly useful for large-scale Power BI models where memory consumption and query performance are critical.

    Metadata Documentation:

        The function can be used to extract metadata about the storage structure for documentation purposes, ensuring that the model's architecture is well-understood and maintained.

        For example, a developer might query this function to create a report or table documenting the storage configuration of a semantic model.

    Troubleshooting Storage Issues:

        If a model exhibits unexpected behavior (e.g., slow queries or high memory usage), this function can provide insights into the underlying storage segments, helping to pinpoint issues like fragmented or oversized segments.

    Integration with Other INFO Functions:

        The output table can be combined with other INFO functions (e.g., INFO.TABLES, INFO.MEASURES, or INFO.VIEW.RELATIONSHIPS) to create a comprehensive view of the model's metadata, aiding in holistic model management.

Example Usage

Since this function is typically used in DAX Query View, here’s an example of how you might query it:

dax

EVALUATE

INFO.GENERALSEGMENTMAPSEGMENTMETADATASTORAGES()

This query returns a table listing all segment map segment metadata storages in the model. To make the output more usable, you could refine it with SELECTCOLUMNS or ADDCOLUMNS:

dax

EVALUATE

SELECTCOLUMNS(

    INFO.GENERALSEGMENTMAPSEGMENTMETADATASTORAGES(),

    "SegmentID", [SegmentID], // Hypothetical column name

    "StorageSize", [StorageSize] // Hypothetical column name

)

Note: The column names (SegmentID, StorageSize) are placeholders, as the exact schema is undocumented. You would need to run the query in DAX Query View or DAX Studio to inspect the actual column names.

Practical Scenario

Imagine you’re managing a large Power BI semantic model with millions of rows, and you notice slow query performance. You suspect that the data segments in the storage engine are not optimized. Using INFO.GENERALSEGMENTMAPSEGMENTMETADATASTORAGES, you can:

    Query the function to retrieve details about segment sizes and configurations.

    Analyze the output to identify segments that are excessively large or improperly configured.

    Use this information to adjust the model’s partitioning strategy or optimize data refresh processes, potentially improving query performance.

Limitations and Considerations

    Undocumented Schema: The lack of detailed Microsoft documentation means you may need to experiment to understand the output.

    Admin Permissions: Only users with semantic model admin rights can use this function, limiting its accessibility.

    Preview Feature Dependency: As of December 2023, DAX Query View (where this function is most useful) is a preview feature, requiring manual activation in Power BI Desktop.

    Not for End Users: This function is highly technical and intended for advanced users or administrators, not typical report developers.

Alternative Tools

If the function’s output is insufficient or hard to interpret, consider using:

    DAX Studio: A free tool that provides detailed model metadata and performance analysis, including access to DMVs that may overlap with this function’s purpose.

    VertiPaq Analyzer: Integrated with DAX Studio, it offers insights into memory consumption and data distribution, which may complement the metadata from this function.

Conclusion

The INFO.GENERALSEGMENTMAPSEGMENTMETADATASTORAGES DAX function is a specialized tool for advanced Power BI users to inspect the storage structure of a semantic model. Its primary use case is in performance optimization, metadata documentation, and troubleshooting for large or complex models. Due to its undocumented nature and technical focus, it’s best used in conjunction with DAX Query View or DAX Studio, and it requires a deep understanding of Power BI’s tabular engine to leverage effectively.