Cost Components for Query Execution

Sorting Techniques

• Sorting relations that fit into main memory typically uses in-memory sorting algorithms, which are efficient due to direct data access.
• For sorting relations that do not fit in main memory, a common approach is the external sorting algorithm, which divides data into smaller units, processes them, and merges them efficiently.

Heuristic Optimization

• The main heuristic to optimize the internal representation in heuristics optimization is selectivity estimation, aiming to minimize the number of retrieved records.
• The first step in the process of heuristics optimization after parsing a high-level query is to generate a query execution plan, which outlines how to execute the query efficiently.

Query Execution Optimization

• To reduce the size of intermediate results, it is often beneficial to apply selection operations first, filtering out unnecessary data early in the execution process.
• The computation cost component in query execution refers to the resources required to execute the operations, often measured in terms of CPU usage and processing time.

Memory Considerations

• The cost component that involves the number of main memory buffers needed during execution is known as the buffer cost component, impacting how data is loaded and accessed.
• Physically ordering records is desirable in query execution because it can enhance performance by reducing I/O operations, facilitating faster data access and retrieval.

Communication Costs

• The communication cost component is associated with the data transfer between different components of the database system, impacting overall query performance.

Efficient Operations

• The operation of join can be implemented efficiently if the input relations are first sorted, enabling faster processing through techniques like merge join.