Finding slow SQL statements

There are two main kinds of slowness that can manifest themselves in a database.

The first kind is a single query that can be too slow to be really usable, such as a customer information query in a CRM running for minutes, a password check query running in tens of seconds, or a daily data aggregation query running for more than a day. These can be found by logging queries that take over a certain amount of time, either at the client end or in the database.

The second kind is a query that is run frequently (say a few thousand times a second) and used to run in single-digit milliseconds, but is now running in several tens or even hundreds of milliseconds, thus slowing down the system. This kind of slowness is much harder to find.

Here, we will show you several ways to find the statements that are either slow or cause the database as a whole to slow down (although they are not slow by themselves).

Getting ready

Connect to the database as the user whose statements you...