Q: “Can you determine what the approximate limits are of: Address Book, Mail, iCal, or other Apple software. I’ve heard that having 15,000 emails is about the limit to Mail, beyond that and you run into trouble. Any thoughts?”
A: The Apple Technical Note found here clearly states that the Maximum File Size is 2 to the 63rd bytes. So clearly its not a file size limitation that is hardcoded.
Practically speaking more than hundreds of anyone of those types of files will slow down the application depending on hardware. I am not sure that you can define hard limits before it becomes unusable. I personally rescued a user whos mail server went down in their company and they had 40,000 message and found it usable on a new macbook pro with 4gb of ram.
I think you could probably chart it if you took into account the average memory requirement of each message and then divided it per messages. For example, Apple Mail I understand takes 4kb to load one email into memory. So using that as a rough figure, you could get about 1.4 million messages theoretically into Mail. I suspect however that Apple would not support that. Apple has repeatedly said they are a consumer company so I would suspect that scaling like this would not be supported. For example, I remember reading something about the kernel being limited to a certain amount of memory so I can’t imagine that it would allow this kind of process to continue.
Personally the less information you put in your apps the better. I think a database that is backed up is a much better way to approach this, and not depend on the client to maintain information. I would not advise anyone relying on backups to manage data over the GB level. It it just not reliable enough to do so. Data deserves more protection than can be found in entry level Apple applications. Filemaker would be my first choice to manage data, and it really makes exporting it a breeze.
(Please note: I am not saying that Apple or the applications are not reliable enough. No single point of failure should be allowed with regard to data. Since hard drives can be damaged or die unexpectedly the idea that you can just back it up on the client I believe is a dangerous one. While I am not totally in favor of the server as the only point where the data resides, I think due to the managed nature of servers it is a better primary place for data. I would like to see data on the client replicated for off-line uses)