How to estimate the effectiveness and usefulness of an index before adding it to production?

To evaluate the effectiveness and usefulness of an index before adding it to production, you can:

• Analyze the query execution plan (EXPLAIN or EXPLAIN ANALYZE) to understand how the index will affect search.
• Use test data similar to real data and run typical queries with and without the index, measuring execution time.
• Assess the impact on write operations: indexes slow down inserts and updates, so it's important to understand the trade-off.
• Check the selectivity of the index — how well it filters data.

Example in PostgreSQL:

EXPLAIN ANALYZE SELECT * FROM orders WHERE customer_id = 123;
-- Add index
CREATE INDEX idx_customer_id ON orders(customer_id);
EXPLAIN ANALYZE SELECT * FROM orders WHERE customer_id = 123;

By comparing the results, you can see how much the index sped up the queries and evaluate its usefulness.