Intelligent query processing in SQL databases

Applies to: yesSQL Server (all supported versions) YesAzure SQL Database YesAzure SQL Managed Instance

The intelligent query processing (IQP) feature family includes features with broad impact that improve the performance of existing workloads with minimal implementation effort to adopt. The following graphic details the family of IQP features and when they were first introduced for SQL Server. All IQP features are available in Azure SQL Managed Instance and Azure SQL Database. Some features depend on the database's compatibility level.

A diagram of the Intelligent Query Processing family of features and when they were first introduced to SQL Server.

Watch this 6-minute video for an overview of intelligent query processing:

For demos and sample code of intelligent query processing (IQP) features on GitHub, visit https://aka.ms/IQPDemos.

You can make workloads automatically eligible for intelligent query processing by enabling the applicable database compatibility level for the database. You can set this using Transact-SQL. For example:

ALTER DATABASE [WideWorldImportersDW] SET COMPATIBILITY_LEVEL = 150;

The following table details all intelligent query processing features, along with any requirement they have for database compatibility level.

IQP features for SQL Server 2022 (16.x) Preview, Azure SQL Database, Azure SQL Managed Instance

IQP Feature Supported in Azure SQL Database and Azure SQL Managed Instance Supported in SQL Server Description
Adaptive Joins (Batch Mode) Yes, starting with database compatibility level 140 Yes, starting in SQL Server 2017 (14.x) with database compatibility level 140 Adaptive joins dynamically select a join type during runtime based on actual input rows.
Approximate Count Distinct Yes Yes, starting in SQL Server 2019 (15.x) Provide approximate COUNT DISTINCT for big data scenarios with the benefit of high performance and a low memory footprint.
Batch Mode on Rowstore Yes, starting with database compatibility level 150 Yes, starting in SQL Server 2019 (15.x) with compatibility level 150 Provide batch mode for CPU-bound relational DW workloads without requiring columnstore indexes.
Cardinality estimation (CE) feedback Yes, starting with database compatibility level 160 Yes, starting in SQL Server 2022 (16.x) Preview with compatibility level 160 Automatically adjusts cardinality estimates for repeating queries to optimize workloads where inefficient CE assumptions cause poor query performance. CE feedback will identify and use a model assumption that better fits a given query and data distribution to improve query execution plan quality.
Degrees of Parallelism (DOP) feedback Yes, starting with database compatibility level 160 Yes, starting in SQL Server 2022 (16.x) Preview with compatibility level 160 Automatically adjusts degree of parallelism for repeating queries to optimize for workloads where inefficient parallelism can cause performance issues. Requires Query Store to be enabled.
Interleaved Execution Yes, starting with database compatibility level 140 Yes, starting in SQL Server 2017 (14.x) with database compatibility level 140 Uses the actual cardinality of the multi-statement table valued function encountered on first compilation instead of a fixed guess.
Memory grant feedback (Batch Mode) Yes, starting with database compatibility level 140 Yes, starting in SQL Server 2017 (14.x) with database compatibility level 140 If a batch mode query has operations that spill to disk, add more memory for consecutive executions. If a query wastes > 50% of the memory allocated to it, reduce the memory grant size for consecutive executions.
Memory grant feedback (Row Mode) Yes, starting with database compatibility level 150 Yes, starting in SQL Server 2019 (15.x) with database compatibility level 150 If a row mode query has operations that spill to disk, add more memory for consecutive executions. If a query wastes > 50% of the memory allocated to it, reduce the memory grant size for consecutive executions.
Memory grant feedback (Percentile) Yes, starting with database compatibility level 150 Yes, starting with SQL Server 2022 (16.x) Preview) with database compatibility level 140 Addresses existing limitations of memory grant feedback in a non-intrusive way.
Memory Grant, CE, and DOP feedback persistence Yes, starting with database compatibility level 160 Yes, starting with SQL Server 2022 (16.x) Preview) with database compatibility level 160 Addresses existing limitations of memory grant feedback in a non-intrusive way by incorporating past query execution to refine feedback. Requires Query Store to be enabled for the database and in "read write" mode.
Optimized plan forcing Yes, starting with database compatibility level 160 Yes, starting with SQL Server 2022 (16.x) Preview) with database compatibility level 160 Reduces compilation overhead for repeating forced queries. For more information, see Optimized plan forcing with Query Store.
Scalar UDF Inlining Yes, starting with database compatibility level 150 Yes, starting in SQL Server 2019 (15.x) with database compatibility level 150 Scalar UDFs are transformed into equivalent relational expressions that are "inlined" into the calling query, often resulting in significant performance gains.
Parameter Sensitivity Plan Optimization Yes, starting with database compatibility level 150 Yes, (Starting in SQL Server 2022 (16.x) Preview) with database compatibility level 150 Parameter Sensitivity Plan Optimization addresses the scenario where a single cached plan for a parameterized query is not optimal for all possible incoming parameter values, for example non-uniform data distributions.
Table Variable Deferred Compilation Yes, starting with database compatibility level 150 Yes, starting in SQL Server 2019 (15.x) with database compatibility level 150 Uses the actual cardinality of the table variable encountered on first compilation instead of a fixed guess.

IQP features for SQL Server 2019 (15.x)

IQP Feature Supported in SQL Server 2019 (15.x) Description
Adaptive Joins (Batch Mode) Yes, starting in SQL Server 2017 (14.x) with database compatibility level 140 Adaptive joins dynamically select a join type during runtime based on actual input rows.
Approximate Count Distinct Yes Provide approximate COUNT DISTINCT for big data scenarios with the benefit of high performance and a low memory footprint.
Batch Mode on Rowstore Yes, starting with database compatibility level 150 Provide batch mode for CPU-bound relational DW workloads without requiring columnstore indexes.
Interleaved Execution Yes, starting with database compatibility level 140 Use the actual cardinality of the multi-statement table valued function encountered on first compilation instead of a fixed guess.
Memory grant feedback (Batch Mode) Yes, starting with database compatibility level 140 If a batch mode query has operations that spill to disk, add more memory for consecutive executions. If a query wastes > 50% of the memory allocated to it, reduce the memory grant size for consecutive executions.
Memory grant feedback (Row Mode) Yes, starting with database compatibility level 150 If a row mode query has operations that spill to disk, add more memory for consecutive executions. If a query wastes > 50% of the memory allocated to it, reduce the memory grant size for consecutive executions.
Memory grant feedback (Percentile and Persistence) Yes, introduced in SQL Server 2019 (15.x) but applies to database compatibility level 140 and higher Addresses existing limitations of memory grant feedback in a non-intrusive way.
Scalar UDF Inlining Yes, starting with database compatibility level 150 Scalar UDFs are transformed into equivalent relational expressions that are "inlined" into the calling query, often resulting in significant performance gains.
Table Variable Deferred Compilation Yes, starting with database compatibility level 150 Use the actual cardinality of the table variable encountered on first compilation instead of a fixed guess.

IQP features for SQL Server 2017 (14.x)

IQP Feature Supported in SQL Server 2017 (14.x) Description
Adaptive Joins (Batch Mode) Yes, starting in SQL Server 2017 (14.x) with database compatibility level 140 Adaptive joins dynamically select a join type during runtime based on actual input rows.
Approximate Count Distinct Yes Provide approximate COUNT DISTINCT for big data scenarios with the benefit of high performance and a low memory footprint.
Interleaved Execution Yes, starting with database compatibility level 140 Use the actual cardinality of the multi-statement table valued function encountered on first compilation instead of a fixed guess.
Memory grant feedback (Batch Mode) Yes, starting with database compatibility level 140 If a batch mode query has operations that spill to disk, add more memory for consecutive executions. If a query wastes > 50% of the memory allocated to it, reduce the memory grant size for consecutive executions.
Memory grant feedback (Percentile and Persistence) Yes, introduced in SQL Server 2019 (15.x) but applies to database compatibility level 140 and higher Addresses existing limitations of memory grant feedback in a non-intrusive way.

For complete details on all IQP features, including release notes and more in-depth descriptions, see Intelligent query processing (IQP) feature details.

See also

Next steps