Apache Spark is well-suited for iterative data processing tasks. It keeps intermediate data in memory, reducing the need to write to disk between stages and significantly improving performance for iterative algorithms. Spark's Resilient Distributed Datasets (RDDs) and in-memory processing make it ideal for scenarios requiring iterative data processing in Hadoop.

Channels in Flume are responsible for storing events until they are consumed by sinks. Channels act as buffers, holding the data between the source and the sink, providing a way to manage the flow of events within the Flume system.

Hadoop Streaming API uses KeyValueTextInputFormat as an interface for data input and output. It allows handling key-value pairs, making it versatile for processing various data types in a streaming fashion.

Cascading's Lingual feature enables the execution of complex join operations in data processing pipelines. Lingual is a SQL interface for Cascading, making it easier to express complex data transformations.

Apache Oozie handles dependencies between multiple Hadoop jobs using a Directed Acyclic Graph (DAG). The DAG defines the order and dependencies between tasks, ensuring that the subsequent tasks are executed only when the prerequisite tasks are completed successfully.

Off-heap memory configuration in a highly optimized Hadoop cluster helps improve garbage collection efficiency. By allocating memory outside the Java heap, it reduces the impact of garbage collection pauses on overall performance.

Ensuring efficient data processing in Hadoop involves focusing on input splitting during development. Input splitting is the process of dividing input data into manageable chunks, allowing parallel processing across nodes and optimizing job performance.

When a MapReduce job fails in Hadoop, the first step is typically to examine the logs. Hadoop generates detailed logs that provide information about the failure, helping developers identify the root cause and take corrective actions.

Snappy compression codec in Hadoop is known for providing a good balance between compression ratio and speed. It offers relatively fast compression and decompression while achieving a reasonable compression ratio, making it suitable for various use cases.

In HDFS, data is read and written sequentially. Hadoop optimizes for large-scale data processing, and reading data sequentially enhances performance by minimizing seek time and maximizing throughput. This is particularly efficient for large-scale data analytics.