| Making sense out of SUSE's delta releases |
May 01, 2006
With a cold on one side and a complete Internet connection meltdown on the other, I've been having a heck of a time keeping up with my email. Still, before my ISP, Bell South, hosed my DSL connection and my cold medicine knocked me out, I got a message asking: "What's the deal with those 'delta' releases for SUSE 10.1? I can't get them to work."
After a little back and forth with him, I saw what his problem was. He thought the delta was the complete distribution. Nope.
A "delta" to a program, in and of itself, is no good to man or beast. It's simply the code of the changes between one version of a program and another. To make use of a SUSE 10.1 delta, you first have to have a copy of the original code. You then apply the delta to that code to create the complete new version of the program, or in this case, the latest version of SUSE 10.1
The term "delta" is often used for this purpose in software configuration circles. Since outside of programming circles, this usage is barely known, I can easily understand why the guy who emailed me was puzzled.
There are several points to using deltas. For developers, it's a means of keeping around different attempts to improve on an existing code base. I might try using a do...while loop to solve a programming problem in one delta of my program while trying an if...then construction in another delta. I can then check them both to see which works better.
On bigger projects, incremental deltas -- or "diffs" as I called them, when I was a programmer -- like the ones SUSE is using, are also useful because they're faster to transport over the net. Instead of requiring everyone to download all five CDs worth of the combined old and new code, SUSE is only providing the delta of the changes between SUSE 10.1 release candidate 1 or 2 and the latest release candidate 3. Instead of spending hours downloading the revised distribution, users spend only minutes getting the latest and greatest.
(Editor's note: Incidentally, SUSE's YAST online updates work this way too, which saves a lot of download time and disk space.)
The flip side is that once you have the delta, you need to apply it to your existing files and then burn a new CD or DVD. Applying these deltas, thanks to SUSE's instructions and programs, isn't that much trouble.
You should however, have the original ISOs on your hard drive. Yes, you can do with your CDs or DVD, but boy is that slow.
You should also make sure you have ample room on your hard drive. Adding binary diffs to an ISO, can take up gigabytes of temporary file space on your drive.
As you might guess from all that drive activity, creating a new ISO file using diffs can be a slow process. Personally, I only use my fastest system" -- currently a Gateway 835GM with an Intel Pentium D 2.8GHz dual-core processor, 1GB DDR2 (double data rate) DRAM, and a fast 250GB 7200RPM with 8MB cache SATA hard drive -- for the job.
Frankly, unless you're a hard core beta tester or you really must have the newest of the new, I think it's too much trouble to bother with. The diff downloads are certainly fast, but I find that creating the revised ISOs, burning them to CDs or DVDs, and then reinstalling the operating system every week just isn't worth it.
For me, SUSE 10.1 RC 1 will be good enough until the day SUSE 10.1 goes final. Come that day, if there are diffs for jumping from RC1 to the final, I'll download them, but in the meantime I'm going to devote what energy I have left from fighting my cold to fighting with my ISP.
-- Steven J. Vaughan-Nichols
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