What's New in Query Optimization in SQL Server 2022: A Deep Dive

Introduction

SQL Server 2022 brings significant advancements to its query processing engine, delivering intelligent performance improvements that can dramatically accelerate your workloads without requiring code changes. In this post, we'll explore the most exciting optimization enhancements that make this release a game-changer for database professionals.

1. Parameter Sensitive Plan (PSP) Optimization

The Problem: The "parameter sniffing" dilemma where a single cached plan performs poorly for different parameter values.

The Solution: SQL Server 2022 now automatically maintains multiple active plans for a single parameterized query when it detects significantly different data distributions.

-- SQL Server 2022 will cache different plans for:
EXEC GetOrdersByStatus @Status = 'Pending'; -- Few rows
EXEC GetOrdersByStatus @Status = 'Completed'; -- Millions of rows

Key Benefits:

• Eliminates the need for OPTION(RECOMPILE) or plan guides

• Handles data skew automatically

• Reduces "bad plan" performance issues

2. Memory Grant Feedback Persistence

Evolution: Memory grant feedback (introduced in 2017) now persists across database restarts.

How It Works:

-- First execution (under-allocates memory):
SELECT * FROM LargeSalesData ORDER BY SaleDate DESC;

-- Subsequent executions remember past memory needs
-- and adjust grants accordingly

Impact:

• 39% fewer spills to tempdb in Microsoft's internal testing

• More stable performance after failovers/restarts

• Works for both over- and under-estimated grants

3. Cardinality Estimation Improvements

New CE Model: Builds on the 2014/2019 estimator with better handling of:

• DISTINCT counts in correlated subqueries

• JOIN containment assumptions

• Predicate combinations (AND/OR logic)

Example Improvement:

-- Better estimates for:
SELECT * FROM Orders o
WHERE o.Status = 'Shipped'
AND (o.Total > 1000 OR o.Priority = 1)

4. Optimized Plan Forcing

New Capability: Query Store now supports forcing parameterized plans.

Implementation:

-- Force a plan while preserving parameterization
EXEC sp_query_store_force_plan @query_id, @plan_id;

Advantages:

• Safer than traditional plan forcing

• Works with PSP optimization

• Maintains security benefits of parameterization

5. Parallel Table Variable Processing

Breakthrough: Table variables can now benefit from parallel execution.

Before (Serial Only):

DECLARE @TempOrders TABLE (OrderID INT, ...);
INSERT INTO @TempOrders SELECT ... FROM LargeTable;
-- Processing always single-threaded

After (Parallel Possible):

DECLARE @TempOrders TABLE (OrderID INT, ... INDEX IX_OrderID);
INSERT INTO @TempOrders SELECT ... FROM LargeTable;
-- May use parallel threads if beneficial

Requirement: Must create an index on the table variable.

6. Enhanced Approximate Count Distinct

New Function: APPROX_COUNT_DISTINCT now handles multiple columns.

Usage:

-- Fast distinct counts across multiple columns
SELECT APPROX_COUNT_DISTINCT(CustomerID, ProductID) 
FROM LargeSalesTable;

Performance: Up to 20x faster than exact COUNT(DISTINCT) on large datasets.

7. Intelligent Query Processing Enhancements

Expanded Features:

• DOP Feedback: Adjusts degree of parallelism over time

• Optimized Skew Handling: Better parallel distribution for skewed data

• Memory-optimized TempDB Metadata: Reduces contention

Practical Recommendations

1. Upgrade Testing: Use Query Store to compare pre/post-2022 plans

2. Adoption Path:

   -- Start with compatibility level 160
   ALTER DATABASE YourDB SET COMPATIBILITY_LEVEL = 160;
   
   -- Monitor with new DMVs
   SELECT * FROM sys.dm_exec_query_optimizer_memory_gate;
   

3. Monitoring: Track new performance counters:

   • PSP cache hits/misses

   • Memory grant feedback adjustments

   • Approximate count distinct accuracy

Conclusion

SQL Server 2022's query optimizer represents Microsoft's most significant investment in years, addressing long-standing pain points while introducing intelligent adaptive behaviors. These enhancements deliver out-of-the-box performance gains that previously required manual tuning, making this release particularly valuable for complex workloads with diverse query patterns.

Pro Tip: The real magic happens when these features work together - PSP optimization with memory grant feedback persistence, for example, creates a self-tuning system that continuously improves.

Have you tested SQL Server 2022's query optimizations? Share your before/after performance comparisons in the comments.