Optimization

Your API handles 50,000 requests per second, and each request executes the same customer lookup query. Profiling shows 15% of CPU time is spent translating LINQ expressions to SQL, not actually running the database query.

This is where EF Core compiled queries shine. They pre-compile the LINQ-to-SQL translation, eliminating that CPU overhead for frequently executed queries.

But compiled queries aren’t a magic performance solution. They have specific use cases and trade-offs that many developers misunderstand.

How EF Core Query Compilation Works

Every time you execute a LINQ query, EF Core goes through several steps:

1. Parse the LINQ expression tree
2. Translate LINQ to database-specific SQL
3. Cache the translation result
4. Execute the SQL query

// Normal query - goes through full pipeline every time
var customer = await context.Customers
    .Where(c => c.Id == customerId)
    .Include(c => c.Orders)
    .FirstOrDefaultAsync();

EF Core caches query plans, but complex LINQ expressions still require parsing and validation on each execution. For simple queries executed thousands of times per second, this overhead becomes significant.

Compiled Query Implementation

Compiled queries pre-compile the LINQ expression, skipping steps 1-2 on subsequent executions:

public static class CompiledQueries
{
    // Compiled query with single parameter
    public static readonly Func<CustomerContext, int, Task<Customer>> GetCustomerById =
        EF.CompileAsyncQuery(( …