Porting Progress Applications to Linux

An explanation of the work required to take an existing Progress application and deploy it on Linux, and the advantages and disadvantages of doing so.
Porting Existing Applications

Since the front end (application) and the back end (the database) are so independent, let's examine what needs to be done one step at a time.

To move an existing Progress character-based application, the good news is all it takes is a recompile. That's it! In fact, there are some instances in which you don't even have to recompile; if you are staying within the same machine class, the same r-code (compiled code) can just be copied from one machine to another and it will run. This is because Progress r-code is not truly compiled code, but rather an interpreted binary format. As long as you remain within the same machine class (defined as machines with the same byte alignment, endianness, and word size), your compiled code will not even need a recompile.

The only time any complications in this process will occur is when you have OS-specific code within your application. Progress code doesn't care what OS it runs on, but if you make a call to an external routine (such as ps with flags specific to your old OS), you will need to make those modifications. However, this situation is fairly rare. Common operating system functions (such as file copy and delete) can be handled generically within Progress by using statements like OS-COPY which work regardless of the underlying platform.

In some circumstances, porting an existing database is just as easy. Officially, Progress does not support copying a database between operating systems or machine architectures. In order to do this, you must do a dump and load. This is a process of extracting the structure and all the data from the database in an ASCII form, then copying the ASCII data to the new machine and loading it into the new database. However, there is an unsupported loophole which I take advantage of regularly. Currently, I dual-boot my laptop with NT and Linux, and I have a Progress database on an NT FAT drive which is visible when I boot Linux. This database is accessible from either OS. I have application code (uncompiled because that is more convenient for me, but I could also share a compiled version) which accesses this database no matter which choice I make at boot time. There can't be much better proof than that. The true technical limitations on copying databases are much the same as those for copying compiled code: if the machine architecture and the word size are the same, you should be okay.

If your situation does require a dump and load, and you want the time your application is unavailable to be as short as possible, there are some techniques which will dramatically reduce the down time of your database. I regularly travel to customer sites and have seen some extreme examples of this: one database, with a size measurable in tens of gigabytes, was unavailable for only 45 minutes and only in the final phase of their dump and load.

This sort of performance, however, requires some custom work in advance. Generally, it involves dumping and loading stable data ahead of the actual cutover point; the greatest time savings occurs when you can define stable data most broadly. For example, if you have modification dates on a table, the entire table can be dumped and loaded in advance; then, when you are ready to cut over to the new system, re-dump only those records modified since the first dump.

A Good Match

Porting an existing character application written in Progress is remarkably simple. With over 5000 applications already written, the arrival of Progress on the Linux scene should make a large dent in the “Linux has no application” argument. Progress is flexible enough in its deployment capabilities that it allows Linux to be integrated into existing deployments transparently to provide greater scalability and cost-effectiveness.

Tom Barringer is a Senior Consultant with Progress Software. He is most commonly found in airport lounges or in front of classrooms. What he does in his spare time is yet to be determined because he rarely has any. However, thanks to the wonders of modern technology, he can usually be reached at tomb@progress.com.