Identifying Performance of MySQL Indexing

When optimizing MySQL queries, it's crucial to assess the effectiveness of indexing.

Obtaining Indexing Performance Metrics

To determine whether your query uses an index, execute the following query:

EXPLAIN EXTENDED SELECT col1, col2, col3, COUNT(1) 
FROM table_name 
WHERE col1 = val 
GROUP BY col1 
ORDER BY col2;

Subsequently, run:

SHOW WARNINGS;

If the "Using index" message appears, the query is utilizing an index. If not, your query does not benefit from index usage.

Optimizing Indexing for Performance

To enhance query performance further, consider implementing covering indexes. These indexes encompass all columns used in the query's WHERE, GROUP BY, ORDER BY, and SELECT clauses.

For the sample query provided, you could create a covering index using:

KEY(col1, col2, col3)

This ensures that the table scan will retrieve all necessary data without additional I/O operations, improving query speed significantly.

Note: While indexing improves query performance, it can potentially impact the efficiency of insert queries.