Impala supports Vectorized Query Execution as an advanced feature for optimizing distributed queries. This technique processes data in batches, leveraging CPU SIMD (Single Instruction, Multiple Data) instructions for better performance, especially in analytics and data processing tasks.

The primary tool used for debugging Hadoop MapReduce applications is the Hadoop Debugging Tool. It helps developers identify and troubleshoot issues in their MapReduce code by providing insights into the execution flow and intermediate outputs.

Hadoop Streaming API can be integrated with Apache Spark for enhanced performance in complex data processing tasks. Spark provides in-memory processing, which significantly improves the speed of data processing compared to traditional batch processing frameworks.

The integration of Scala with Hadoop is often facilitated through the Apache Flink framework for distributed computing. Flink is designed for stream processing and batch processing, providing high-throughput, low-latency, and stateful processing capabilities.

After receiving the sorted output from the Mapper, the Reducer in MapReduce performs aggregation. It combines the intermediate key-value pairs based on the keys, producing the final output. This phase is crucial for summarizing and processing the data.

The ApplicationMaster in YARN architecture is responsible for dividing the job into tasks and scheduling them on different nodes. It negotiates resources with the ResourceManager and manages the execution of tasks.

In the context of handling memory-intensive applications, garbage collection is crucial in advanced Hadoop tuning. Efficient garbage collection helps reclaim memory occupied by unused objects, preventing memory leaks and enhancing the overall performance of Hadoop applications.

In a scenario of uneven data distribution, implementing the optimization strategy of Data Shuffling is essential. Data Shuffling redistributes data across the cluster to achieve a more balanced workload, preventing hotspots and ensuring efficient parallel processing in a Hadoop cluster.

For analyzing web log data in Hive, using the ORC (Optimized Row Columnar) storage format is optimal. ORC is highly optimized for read-heavy workloads, offering efficient compression and predicate pushdown, resulting in improved query performance.

In YARN, ApplicationMaster is a critical process that optimizes the use of resources across the cluster. It negotiates resources with the ResourceManager and manages the execution of tasks on individual nodes.