Description

This PR was authored by GitHub Copilot as part of an automated issue triage workflow.

Fixes #5487
Fixes #5702

This PR fixes a memory leak in the LINQ provider where Expression.Compile() generates JIT-compiled DynamicMethods that persist in native memory, causing growth in long-running services.

Root Cause

Location: Microsoft.Azure.Cosmos/src/Linq/SubtreeEvaluator.cs:119-120

Analysis:
Expression.Lambda().Compile() emits a new DynamicMethod with generated IL on every call. DynamicMethod IL is stored in native memory (not GC-tracked), causing memory growth in long-running services with repeated LINQ query evaluation.

Evidence:

// Before (problematic) - SubtreeEvaluator.cs:119-120
Delegate fn = Expression.Lambda(expression).Compile();
return fn.DynamicInvoke(null);
// Each call emits new DynamicMethod IL to native memory

Changes Made

Call sites updated (4 files)

• SubtreeEvaluator.cs EvaluateConstant(): original leak site (LINQ provider, the SDK continuously generates new JIT-compiled DynamicMethods (resulting in unmanaged memory growth) #5487)
• Utilities.cs ExpressionSimplifier<T>.Eval(): uses generic overload, no cast needed
• DocumentQueryEvaluator.cs HandleAsSqlTransformExpression(): 2 Compile() calls
• GeometrySqlExpressionFactory.cs Construct(): uses generic overload, no cast needed

SubtreeEvaluatorBenchmark.cs (new)

• Added BenchmarkDotNet benchmark in the Performance.Tests project with [MemoryDiagnoser]
• CompileBaseline: duplicates old lambda.Compile() code path
• EvaluateWithFix: calls actual SubtreeEvaluator.Evaluate() to measure the real fix
• NativeCompileMemoryGrowth: runs 1000 iterations of old Compile() demonstrates unbounded memory growth
• InterpretedCompileMemoryGrowth: runs 1000 iterations of fix path demonstrates stable memory

Benchmark Results

Environment: Windows, .NET 8.0, Release build, ARM64

Performance (per-call)

Why this validates the fix:

• The ~15x speedup proves IL emission + JIT compilation is being skipped
• Compile() must generate IL and JIT-compile (~44μs overhead)
• Compile(preferInterpretation: true) interprets directly (~3μs overhead)
• No native memory growth from DynamicMethod allocation

Testing

Local Validation

Breaking Changes

None

External References

• Issues: LINQ provider, the SDK continuously generates new JIT-compiled DynamicMethods (resulting in unmanaged memory growth) #5487, LINQ: Apply Compile(preferInterpretation) fix to remaining Expression.Compile() call sites #5702
• Related community PR: [Internal] LINQ: Fixes unbounded JIT/IL growth in SubtreeEvaluator by using interpreted expression compilation #5488 (similar fix by issue reporter)
• .NET Docs: Expression.Compile(preferInterpretation)

Checklist

• Code follows project conventions
• Self-review completed
• Comments added for complex logic
• Documentation updated (if applicable)
• New tests added for the fix
• All existing tests pass (local)
• Remote CI gates pass (monitoring)

Generated by GitHub Copilot CLI Agent