spørringsplanleggeren

The Norwegian term "spørringsplanleggeren" translates to "query planner" in English. It is a fundamental component of database management systems (DBMS) responsible for determining the most efficient way to execute a given SQL query. When a user submits a query, the query planner analyzes it, considering various execution strategies.

The query planner's primary goal is to minimize the resources, such as CPU time and I/O operations, required to retrieve the requested data. It evaluates different access paths, join methods, and data ordering techniques. For instance, it might decide whether to use an index scan or a full table scan, or if a nested loop join or a hash join would be more appropriate for combining data from multiple tables.

To make these decisions, the query planner relies on statistics about the data stored in the database, such as the number of rows in tables, the distribution of values in columns, and the presence of indexes. Based on these statistics and an internal cost model, it estimates the cost of each potential execution plan and selects the one with the lowest estimated cost.

The effectiveness of the query planner significantly impacts the overall performance of a database. A well-optimized query plan can result in much faster query execution, while a poorly chosen plan can lead to slow response times and resource contention. Database administrators often tune database schemas and statistics to help the query planner make better decisions.