Entity Framework Core (EF Core) is an open-source, lightweight, extensible, and cross-platform version of the popular Entity Framework data access technology. It is used for mapping database objects to .NET objects, allowing developers to work with a database using .NET objects rather than raw SQL.

EF Core improves performance through various optimizations such as compiled queries, batching of commands, and better memory management. It also supports more efficient querying strategies and provides tools for analyzing and optimizing queries.

Compiled queries in EF Core are pre-compiled versions of LINQ queries that can be reused multiple times. This reduces the overhead of parsing and planning the query each time it is executed, leading to improved performance.

To optimize performance, you can:

• Use compiled queries.
•  Avoid lazy loading when not necessary.
• Use no-tracking queries for read-only operations.
• Minimize the use of Include and Select only necessary fields.
• Utilize indexes and ensure your database schema is optimized.
• Use raw SQL queries for complex operations.

Eager loading loads related data as part of the initial query, which can result in more efficient queries by reducing the number of database calls. Lazy loading, on the other hand, loads related data only when it is accessed for the first time, potentially causing multiple database calls and impacting performance.

You can use raw SQL queries in EF Core with the `FromSqlRaw` or `FromSqlInterpolated` methods. These methods allow you to execute raw SQL queries and map the results to your entity classes. This can be useful for complex queries that are difficult to express with LINQ.

Common pitfalls include:

•  Overusing lazy loading, leading to the N+1 query problem.
• Not optimizing the database schema.
• Ignoring the use of proper indexes.
• Failing to handle concurrency conflicts.
• Mismanaging transactions and connection lifetimes.

EF Core provides mechanisms for handling concurrency conflicts using optimistic concurrency control. You can configure your entities to use concurrency tokens, such as a timestamp column, and handle conflicts by catching `DbUpdateConcurrencyException` and resolving conflicts as needed.

Migrations in EF Core are used to manage changes to the database schema over time. They provide a way to apply incremental updates to the database structure, keeping it in sync with the application's data model. Migrations can be created, applied, and rolled back using EF Core tools.

You can measure the performance of your EF Core queries using tools such as the `DbContext.Database.Log` property, SQL Server Profiler, or third-party profiling tools. To improve performance, analyze query execution plans, optimize indexes, use compiled queries, and refactor inefficient LINQ queries.