What is the difference between using an index and a read-only index in databases?

An index in a database is a data structure that speeds up data search and retrieval. An index can be read-only or for writing.

Read-only index is usually created to optimize queries when data does not change or changes are not expected. Such an index is not updated when data changes, which reduces overhead for maintaining the index but is not suitable for tables with frequent updates.

Regular index is maintained and updated during insertions, updates, and deletions, allowing it to be used to accelerate queries in dynamically changing tables.

Thus, the main difference:

• Read-only index does not update when data changes, increasing read performance but limiting its use.
• Regular index is maintained and updated, ensuring data relevance but with additional costs for updates.