CodeIgniter supports RESTful controller methods by extending the REST_Controller class. This class provides functionality to handle HTTP methods like GET, POST, PUT, and DELETE in a RESTful manner. It streamlines the process of building RESTful APIs in CodeIgniter.

The principle of least privilege in advanced database security advocates granting the minimum necessary access rights to users or processes. By adhering to this principle, the risk of SQL injection is mitigated, as users and processes are only given the specific permissions required for their legitimate tasks, reducing the attack surface and potential impact of SQL injection attacks.

It's good practice to include version information in the header of the library file. This ensures proper version tracking and compatibility checks.

CodeIgniter ensures data integrity during transactions by employing foreign key constraints. Foreign key constraints establish a relationship between tables, ensuring that the values in a column (or columns) of one table match the values in another table's primary key. When a transaction involves multiple tables with foreign key relationships, CodeIgniter ensures that the foreign key constraints are satisfied, maintaining the consistency and integrity of the data across tables. Foreign key constraints prevent actions that would compromise the referential integrity of the database.

When integrating a third-party library into a CodeIgniter application, it's crucial to consider the version compatibility. This ensures that the third-party library is compatible with the specific version of CodeIgniter and its features, preventing potential issues and conflicts.

Using a third-party cloud service for file storage enhances security by mitigating the risk of data loss. Storing files externally reduces the impact of server-related issues and provides better scalability and reliability.

Before replacing core library functions, it's crucial to identify the dependencies of the existing functions. This involves understanding which parts of the application rely on the current functionality. This step helps prevent unintended consequences and ensures a smooth transition to the custom library.

When replacing a native library with a third-party one for performance optimization, compatibility with future CodeIgniter versions is crucial. This ensures that the application remains maintainable and can benefit from future updates without major disruptions.

In the Active Record Class of CodeIgniter, the update() method is used to update an existing record in the database. This method allows you to set new values for the fields of a record based on certain conditions. It simplifies the process of updating records by abstracting the underlying SQL queries and providing a more convenient and readable way to perform database updates.

CodeIgniter simplifies the handling of complex XML structures through its XML Parser Class. This class allows developers to easily parse and manipulate XML data within their applications, providing a convenient way to work with XML content.

In complex applications, Continuous Integration (CI) is used to automatically run unit tests in different environments. CI systems like Jenkins or Travis CI integrate seamlessly with CodeIgniter, automatically triggering unit tests upon code changes. This ensures consistent code quality and identifies issues early in the development cycle.

The logging level ALL in CodeIgniter includes error messages, debug messages, and informational messages, providing a comprehensive view of the application's log.