Does a B-tree index always improve performance, or can the opposite happen?

A B-tree index usually improves query performance, especially for searches, sorting, and range queries, due to logarithmic access time. However, there are situations where using a B-tree index can lead to performance degradation:

• Small tables: For very small amounts of data, a full table scan might be faster than using an index because of the overhead of traversing the tree.

• High selectivity: If queries return a large portion of the table, using an index may be inefficient, as it requires many lookups by pointers.

• Frequent updates: Indexes require additional time to update during inserts, deletes, and modifications. In systems with intensive data changes, this can slow down write operations.

• Inappropriate query types: For example, queries with functions or operations that cannot utilize the index (like LIKE '%abc') will not benefit from a B-tree index.

Thus, a B-tree index does not always improve performance, and its use should be justified by the nature of the data and queries.