Advanced MapReduce jobs often require Apache Spark to manage complex data dependencies and transformations. Apache Spark provides in-memory processing and a rich set of APIs, making it suitable for iterative algorithms, machine learning, and advanced analytics on large datasets.

In the case of frequent data processing slowdowns, prioritizing Hadoop performance monitoring using tools like Ambari is crucial. Ambari provides a comprehensive view of cluster health, performance metrics, and allows for efficient management and troubleshooting to identify and address performance bottlenecks.

Profiling is a technique used in complex Hadoop applications to identify and isolate performance bottlenecks. It involves analyzing the execution of the code to understand resource utilization, execution time, and memory usage, helping developers optimize performance-critical sections.

Python is commonly used for writing scripts that can be processed by Hadoop Streaming. The flexibility of Hadoop Streaming allows the use of scripting languages, and Python is a popular choice for its simplicity and readability.

For encrypting sensitive data at rest and in transit, Hadoop Transparent Data Encryption (TDE) is a crucial security feature. TDE encrypts data stored in HDFS, adding an extra layer of protection, and ensures that data transferred between nodes is encrypted, safeguarding it from unauthorized access.

Advanced debugging in Hadoop often involves analyzing Log Files to diagnose issues in job execution. Log files contain valuable information about the steps taken during job execution, helping developers identify and resolve issues in the Hadoop application.

For enhanced security in a Hadoop cluster dealing with sensitive information, prioritizing the security of the NameNode is crucial. The NameNode contains metadata and information about data locations, making it a potential target for security threats. Securing the NameNode helps safeguard sensitive data in the cluster.

Parquet enhances query performance through Predicate Pushdown. This strategy involves pushing parts of the query execution directly to the storage layer, reducing the amount of data that needs to be processed by the query engine. This is particularly effective for columnar data storage, like Parquet, where only relevant columns are read during query execution.

In Hadoop, the NetworkTopology is vital for monitoring and managing network traffic and data flow. It represents the physical network structure, helping optimize data transfer by placing computation closer to the data source.

Hadoop employs the strategy of data replication to balance load and ensure data availability across the cluster. Data is replicated across multiple nodes, providing fault tolerance and enabling parallel processing by allowing tasks to be executed on the closest available data copy.

The primary challenge in unit testing Hadoop applications involving HDFS is handling large datasets. Unit testing typically involves smaller datasets, and dealing with the volume of data in HDFS during testing poses challenges. Strategies like using smaller datasets or mocking HDFS interactions are often employed to address this challenge.

A local job runner in Hadoop unit testing simulates the Hadoop environment locally. It allows developers to test their MapReduce jobs on a single machine before deploying them on a Hadoop cluster, facilitating faster development cycles and easier debugging.