Advanced techniques for performance tuning in DB2 include query optimization, which involves analyzing and fine-tuning SQL queries to improve execution efficiency. It often involves creating or modifying indexes, adjusting buffer pool sizes, and using advanced SQL features like common table expressions (CTEs) or window functions to optimize query execution plans. 

User-defined functions can enhance code readability and maintainability in DB2 by encapsulating complex logic, reducing the need for repetitive code, and promoting modular development. Encapsulating logic within functions improves code readability by abstracting implementation details and providing a clear interface for other developers to use. Additionally, modular development facilitates code reuse and simplifies maintenance efforts by isolating changes to specific functions rather than scattering them throughout the application. 

The FETCH statement in DB2 cursor operations retrieves rows from result sets. It is used to fetch the next row or a specified number of rows from the result set associated with a cursor. FETCH allows applications to retrieve and process data row by row, providing control over the data retrieval process. 

In a partitioned database environment, DB2 handles data distribution through hash-based distribution. This approach involves distributing data across partitions based on a hash function applied to one or more columns, known as partitioning keys. Hash-based distribution ensures even distribution of data across partitions, which helps in achieving balanced query processing and optimal performance in parallel processing environments. 

VARCHAR data type in DB2 is suitable for storing textual data of varying lengths, such as names, addresses, or descriptions. It allows for efficient storage and retrieval of character data. 

The DELETE FROM statement in SQL is used to delete all records from a table. It removes all rows from a table without deleting the table itself or its structure. This operation is irreversible, so it's important to use it with caution to avoid accidental data loss. 

DB2 Connect is a software product developed by IBM to allow applications to connect to DB2 databases. While it's versatile in its connectivity, one of its key focuses is integration with cloud systems like AWS and Azure. This integration enables seamless interaction between on-premises DB2 databases and cloud-based applications, fostering flexibility and scalability in the IT infrastructure. Cloud integration ensures that DB2 databases can adapt to modern cloud computing environments, supporting organizations in their journey towards digital transformation. 

Denormalization increases query performance by reducing the number of joins required to retrieve data. By storing redundant data, it eliminates the need for joins, thus improving performance. 

In Flutter, the handling of user input events varies between web and desktop applications. For web, mouse events like onTap and onClick are commonly used, whereas desktop applications often rely on keyboard events. Understanding these differences is crucial for developing cross-platform Flutter applications that provide a consistent and intuitive user experience across various devices.

When optimizing a Flutter application for both web and desktop, a performance issue may arise due to platform-specific widgets. Flutter provides a set of widgets optimized for each platform, and using them incorrectly or inefficiently can impact performance. Developers must carefully choose and customize widgets based on the target platform to ensure optimal performance on both web and desktop. Optimizing UI elements for different platforms is crucial for a smooth user experience.