Analytics Ssas 2025

Further improvements to parallel DirectQuery (building on SSAS 2022):

• Parallelizes multiple queries to the data source for a single DAX query
• Better handling of data source delays and network latency
• Combined with Horizontal Fusion: fewer queries, each running in parallel, for maximum throughput

MDX + Calculation Groups Performance

Significant performance improvements for MDX queries on models that use calculation groups and format strings.

• Reduced memory usage for these query patterns
• Improved responsiveness
• Benefits organizations using calculation groups (SSAS 2019+) with MDX-based reporting tools (Excel PivotTables, SSRS)

Selection Expressions

Extends the calculation groups feature (introduced in SSAS 2019) with finer-grained control:

• Selection expressions provide control over calculation behavior when multiple calculation items are selected simultaneously
• No-selection behavior defines logic for when no specific selection is made on a calculation group
• Enables more sophisticated calculation group patterns without workaround DAX measures
• Requires compatibility level 1700

Independent Value Filters

New option to control value filter behavior in the engine:

• Prevents automatic combining (coalescing) of multiple filters on the same table into a single filter
• Provides greater flexibility for precise, independent filtering in complex models
• Addresses edge cases where coalesced filters produced unexpected results

DAX Language Enhancements

LINEST and LINESTX:

• Perform linear regression using the Least Squares method
• Calculate the straight line that best fits given data points
• Enables statistical analysis directly within DAX without external tools
• LINEST returns a single row; LINESTX is the iterator version for row-by-row calculation

Unicode Surrogate Pair Support:

• Support for expanded Unicode standards including Chinese GB18030 government standard
• Ensures correct handling of supplementary Unicode characters in DAX string operations

Binary XML + Compression

XMLA-based communication improvements:

• Switched from plain text XML to binary XML for XMLA communication
• Compression enabled for .NET client libraries
• Reduces network overhead and improves response times for large result sets
• Transparent to applications -- no code changes required; update client libraries to benefit

Diagnostics Improvements

Execution metrics now exposed through Extended Events and Profiler traces:

• Query execution metrics available via XEvents for detailed performance analysis
• Better visibility into query execution plans and resource consumption
• Enables more precise troubleshooting compared to prior versions

Migration from SSAS 2022

1. Upgrade the SSAS instance to SQL Server 2025
2. Set model compatibility level to 1700 in Visual Studio or Tabular Editor
3. No breaking changes from compatibility level 1600 to 1700
4. Horizontal Fusion and enhanced parallelism activate automatically at compatibility level 1700
5. Selection expressions require compatibility level 1700 -- update calculation groups to use them
6. Update client libraries (ADOMD.NET, MSOLAP) to benefit from binary XML and compression
7. Test all existing DAX/MDX queries and reports after upgrading compatibility level
8. Review XEvents configuration to take advantage of new execution metrics