Updating a production system can often be a harrowing experience. If the system is one which is in use 24 hours a day, or even during normal work hours, it is essential that the downtime be kept to a minimum. You can make things a little easier by using library lists to your advantage.
First of all, you should place a temporary library at the beginning of the production system's library list. This will become a permanent addition to the library list, and serve as a temporary holding place for objects that are to be updated. Be sure to treat this as any other production library, as far as security and so on.
When you wish to make an update, first move the old objects into the temporary library. If it is a program you are updating, you can do this while it is being executed. As long as the temporary library is in the user's library list, the users will not be affected. If it is a file you wish to update, you will need to do this while it is not in use. In any case, it only takes a second to move an object.
Now you can compile the new objects into the production library at your leisure, without worrying that something terrible will go wrong, as the users are standing around waiting for the update to take place. After you are sure that the update has gone successfully, you simply rename the object in the temporary library, and then the users will be using the updated version. Again, if it is a program you are updating, you can do this as it is being executed by the users. Anyone using the program at the time of the rename will be unaffected. When the program is called again, the new version will be used.
You need to use this method only a few times to realize the value of doing it this way. For critical applications, program changes can be made while the system is still up and running. For changes to files, downtime is kept to an absolute minimum, and there are never any surprises.
Editor's Note: Keep in mind that if you use this technique, all versions of library lists referenced by the production library programs must have the temporary library added to them. For example, a library list that is referenced via a job description must include the temporary library.
Jon Vote Medford, Oregon
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