The “slow query log” is the single most valuable way to examine query execution on your MySQL server. Queries are logged with timing information, and in the case of Percona Server, a great deal of additional performance and other diagnostic information. But the execution time recorded in the log is the time the query took on the server, and the client that sent the query to the server might see something quite different. Sometimes it’s valuable to be able to see both views of query execution time.

Why would you want to see the query timing information from the application server or other client program? I have run into a handful of scenarios where this was desirable. For example, sometimes there is no access to the database server. I’ve seen this when access was forbidden by management, and when a server was so overloaded that nobody could get into it if they wanted to. Another reason for logging from the client is to log only …

Sometimes you just need some data to test and stress things. But randomly generated data is awful — it doesn’t have realistic distributions, and it isn’t easy to understand whether your results are meaningful and correct. Real or quasi-real data is best. Whether you’re looking for a couple of megabytes or many terabytes, the following sources of data might help you benchmark and test under more realistic conditions.

• The venerable sakila test database: small, fake database of movies.
• The employees test database: small, fake database of employees.
• The Wikipedia page-view statistics database: large, real website traffic data.
• The …