Getting Your Marching Orders

When you are evaluating a new tuning assignment, you need to get examples of specific problems that you are to solve. Many times you'll just hear a very unspecific "the system's slow," but often you'll be presented with a detailed laundry list of problems with the system. Typical things that you'll see are:

• Performance slowing down

• System hangs or freeze up

• System crashes

• Specific queries take too long

• Random errors

• Jobs failing "for no reason"

• Contention errors

• Extent sizing problems

Unfortunately, these errors do not always come with neat little labels on them that tell you where they come from. For example, poor UNIX kernel configuration can result in seemingly random errors that seem to make no sense. Usually, a system's owners and users have the best instincts for the system's problems. Listen to them. They're a great resource. Get them to prioritize the problems, so that you can work on the most important issues.

It's important to establish an understanding about ground rules on the system. If you're on a production system, you need to know the rules about anything that will impact production work. Negotiate on this. In order to tune a production system properly, you will have to impact production to some extent. Make sure that whoever is signing your check knows this and is prepared for it. In any tuning exercise, it's possible that you'll stumble onto a bug or underlying problem that nobody expects. There's a possibility that you'll take the whole system down to such an extent that you'll have to recover from backups or even have to reinstall the operating system from scratch. This is a worst-case scenario, but you need to prepare for it. Make sure that you have access to all of the people and/or passwords that you need for the duration of the tuning effort. On a UNIX system, you will at least need the Informix user password. If you can get the root password, so much the better. Many of the utilities you'll use to inspect kernel parameters require root access. If you can't get root access, get access to the system administrator. If you're working on the system after hours, know how to get hold of anyone you need.

The underlying idea behind this stage is to set your and your client's expectations properly for the coming tuning task. You need to know what's needed by the client, and your client needs to know what's possible and what to expect.