We're running into a situation where Core Data is making very large
memory allocations when faulting in small amounts of data.
The entity has:
- 2x Date
- Int16
- 4x Int32
- Boolean
- String
- to-one relationship
- String (in a subentity)
- to-one relationship (in a subentity)
- to-many relationship (in another subentity)
Those should be ~128 bytes on 32 bit.
But when these are faulted in, according to Instruments, Core Data
allocates a GeneralBlock-528384 per record! Even if you naively
preallocated a good chunk of memory for the strings, I can't imagine
using more than 1-2KB per record, so 516KB is totally ridiculous.
The stack trace is:
5 <our code>
4 CoreData -[_NSFaultingMutableSet objectEnumerator]
3 CoreData -[_NSFaultingMutableSet willRead]
2 CoreData -[NSManagedObjectContext(_NSInternalAdditions)
_retainedObjectWithID:optionalHandler:withInlineStorage:]
1 CoreData +
[NSManagedObject(_PFDynamicAccessorsAndPropertySupport)
allocWithEntity:]
0 CoreData _PFAllocateObject
This is allocating an object across a to-many relationship. A 516KB
allocation for a single managed object is wrong. It would require
your entity have over 100,000 properties, and the limit is 2^15
properties per entity.
It could be a bug in Core Data, or a memory smasher in your app that
corrupts either our data structures or the ObjC runtime structures.
Or the stack trace here could be computed incorrectly. If the stack
trace were off slightly, then a hypothetically reasonable allocation
would be for the CFSet holding the contents of the to-many
relationship, assuming it had 50-100 thousand entries.
malloc_history and libgmalloc (see man page) may help produce some
more information.
If you can reproduce this in a sample project with your model, you
should definitely file a bug. If you can attach your program and
steps to reproduce, you could file a bug with that as well.
- Ben
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