MySQL performance diagnostics

MySQL Slow Query Tester

Benchmark a MySQL or MariaDB SELECT query, measure its execution time and identify common performance issues such as full scans, missing filters and large result sets.

Query performance test

Enter your database and SQL query

Connect to the selected database and run a controlled performance test against a SELECT statement.

Live benchmark

Running slow query test...

Database connection

Enter the connection details for the MySQL or MariaDB database containing the tables used by your query.

IP address or hostname Database server

Port number Normally 3306

Database name Database to test

Database username SELECT access required

Database password Password for the database user

SQL query

Enter the SELECT query you want to benchmark. Keep the result set reasonably small while testing.

SQL query to test SELECT queries only

The tester measures how long the supplied query takes to execute and may preview a limited number of returned rows.

Submit SELECT queries only. Do not use INSERT, UPDATE, DELETE, DROP, ALTER, TRUNCATE or other statements that can modify database data or structure.

Complex queries can place significant load on a live database. Test carefully and avoid running expensive benchmarks during busy broadcast or production periods.

What this tool checks

Query execution time
Number of returned rows
Large or unrestricted result sets
Missing WHERE conditions
Missing LIMIT clauses
Expensive sorting or grouping
Query result preview

What counts as slow?

A query that feels slow depends on how often it runs, how many rows it examines and whether it blocks other work.

A query taking one second may be acceptable when run occasionally but problematic when executed several times each second.

Compare results under similar server load and with realistic production data.

WHERE and LIMIT

A missing WHERE clause can force MySQL to inspect every row in a table.

A LIMIT clause can reduce the number of rows returned, but it does not always reduce the amount of work needed to find and sort them.

Filter using indexed columns where practical.

Sorting and grouping

ORDER BY and GROUP BY can become expensive when the database cannot use a suitable index.

Sorting large result sets may require temporary storage or a filesort operation.

Review the query plan when sorting or grouping contributes most of the execution time.

Database caching

Repeating the same query can produce faster times because table and index pages may already be held in memory.

Run several tests and compare the first result with later executions.

Avoid assuming that a cached benchmark represents every real-world execution.

Optimisation tips

Return only the columns the application actually needs instead of using SELECT *.

Add suitable indexes to columns used frequently in WHERE and JOIN conditions.

Avoid functions on indexed columns when those functions prevent index use.

Use the Index / Query Plan Helper alongside this tester when a query consistently performs poorly.

MySQL Slow Query Tester

Database connection

SQL query

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