How was the 40% improvement in SQL query performance measured?

Improvement of SQL query performance by 40% is usually measured using execution time benchmarks before and after optimization. For this, query profilers or built-in DBMS tools, such as EXPLAIN ANALYZE in PostgreSQL, can be used to obtain precise execution times.

Example approach:

1. Run the original query several times, record the average execution time.
2. Make optimizations (indexes, rewriting the query, changing the structure).
3. Run the optimized query, record the new average time.
4. Calculate the improvement percentage:

old_time = 1.0  # seconds
new_time = 0.6  # seconds
improvement = ((old_time - new_time) / old_time) * 100
print(f"Improvement: {improvement}%")  # Will output: Improvement: 40.0%

Thus, the measurement is based on comparing execution times before and after optimization.