[Richard Demers>http://www.cincomsmalltalk.com/userblogs/rademers/blogView?showComments=true&entry=3257583820] points out that there will be 18 million billion addresses to store objects in to with 64-bit Smalltalk and he ponders the implications of using that much memory and having that many objects.
So I thought it would be fun to find out just how big most objects are in a typical VisualWorks system. Exclusing arrays, all 'data' objects that link to other objects range from having 0 instance variables up to 72 instance variables.
Number of instance variables in a class vs number of classes that have that number of instance variables:
- 0-5 instance variables: 1852
- 6-10 instance variables: 5069
- 11-15 instance variables: 710
- 16-20 instance variables: 182
- 21-30 instance variables: 97
- 31-72 instance variables: 23
Now, just because there are more classes with low numbers of instance variables doesn't mean they're more likely to be instantiated in a system - but, in general principle, on a hunch, I'd say that's very likely to happen. So we're looking at between 0-15 instance variables per object. Lets err towards 10 instance variables, 8 bytes per pointer, so we're using 80 bytes of memory for an object.
Now, for something more gutsy in our system. How many strings do we have and how much space do they take up? Same for arrays:
- Number of Strings: 111,155
- Size of Strings: 3,230,686
- Number of Arrays: 97,460
- Size of Array (8 bytes per pointer): 746,318 * 8 = 5,970,544
- Number of OrderedCollections: 4,874
- Size of OrderedCollection (8 bytes per pointer): 21,667 * 8 = 173,336
I've got no conclusions to make from this, I was just curious about the shape and nature of memory usage in a typical Smalltalk application. And there we have it.