How does the scheduler mechanism decide when to apply an index in the database?

The database query planner decides when to use an index based on statistics and operation costs. It analyzes available indexes, evaluates how much using an index will speed up searches compared to a full table scan. If the planner determines that using an index will reduce query execution costs (for example, when retrieving a small subset of data), it will use the index. Otherwise, it will perform a full table scan.

This decision depends on:

• The index map and their structure
• Data distribution statistics
• Query filters and conditions

Thus, the planner chooses the optimal execution plan to improve performance.