Behavior that blows my mind -- duplicating restored information

Question

I have an external drive with all my iTunes information. I lost some changes to playlists mid-day today, and got my library to the point where I thought it would just be easier to restore my latest backup from a few hours previous, since I hadn't made any purchases since the last backup.
I disabled TimeMachine backups, so the latest backup was the one I restored from.
First problem: I go to restore the iTunes folder, and only get the choice to delete the old information and restore with new information or to make no changes. What ever happened to just doing an intelligent restore that just fixes what's different?
Second -- and wilder -- problem. So, I decided to erase the external drive (but not repartition or rename it), and restore everything onto the erased partition. When I re-enabled TimeMachine, the first backup BACKED UP ALL 207 GB OF THE RESTORED MATERIAL ALL OVER AGAIN! If TimeMachine just restored it, shouldn't it know it is the same as the material it just restored?
What kind of programming leads to this?
So, over 20% of my backup disk is used for an exact duplicate of material that is already there. The iTunes library is copied twice. (I can tell because the disk space available on my TimeMachine backup drive shrunk by all 207 GB.)

Answer 1

Linda Custer wrote:
I had just asked Time Machine to restore a folder from its most recent backup. It already had all that information. The last time Time Machine looked, the information was there -- that's why it's in the most recent backup. Then I asked it to restore. So everything is JUST as it was in the last backup. It knows that.
No, it doesn't, at least not without comparing everything on both drives every time it does a backup.
One of the big advantages of Time Machine over traditional "archive"-type backups is the speed of incremental backups, because of the way TM works.
If you've ever used such an app, when they do incremental backups, they examine every file and folder on your system to see what's changed and needs to be backed-up. This is, obviously, a very lengthy procedure.
But TM uses an internal database that OSX keeps on each drive, called the File System Event Store, of each directory (folder) that was changed. So TM can just look in that particular directory. When you consider that even a small Mac running OSX has upwards of half a million files and folders, that's clearly a huge advantage.
For example, on my small (~30 gb) system, when very little has changed, CarbonCopyCloner's incremental backup takes 15 - 20 minutes and most of my CPU. My Time Machine backups rarely take over *30 seconds* and I usually notice them only if I happen to see the icon spinning.
The occasional downside of that is, if you replace everything on a disk, it's all changed, even if you put all the same info back.
With a traditional system, it just isn't practical to do incremental backups more than once or twice a day (and they have other large disadvantages, too).
So, take your choice.