Re: Garbage collection, core data, and tight loops

FROM : John R. Timmer
DATE : Sun Nov 04 05:06:24 2007

On Nov 3, 2007, at 8:26 PM, Ben Trumbull wrote:

>> Okay, so for completeness, i thought i'd share the resolution of this
>> with the list, in case someone finds this thread in the future.
>>
>> I set the app up to create small batches of ManagedObjects (several
>> hundred at a time) and added a small pause (0.01 sec.) between 
>> batches
>> via a delayed selector.

>
> You shouldn't need a pause, and you should have good results with 
> batches in the thousands.


Batches of about 350 just turned out to be what i wound up with when 
reading the input file a megabyte at a time.  The pause just helped me 
avoid a recursive call  and set me up for threading things.

>

>> Before creating any ManagedObjects, i cancelled undo registration.
>>
>> Once a batch was created, i processed pending changes, saved, and
>> reset the managedObjectContext.
>>     incidentally, resetting appears to create a brand new undo manager
>> for the context, so i disabled each time; there was no need to re-
>> enable when done.

>
> To disable the undo manager on NSManagedObjectContext, set it to 
> nil.  -reset does not recreate an undo manager.


Interesting.  I disabled it using disableUndoRegistration, and then 
tried to re-enable it after resetting the managedObjectContext, and 
the app logged a complaint that suggested it had already been re-
enabled.

>
>

>> Using an autorelease pool for each batch worked well, keeping memory
>> use extremely low.
>>
>> Using garbage collection resulted in a significant memory gain, but
>> nowhere near bad enough to crash the program.  Oddly, the memory use
>> did not subside after the loop had finished.

>
> How did you measure that ?  'heap' will provide more useful 
> information than 'top'


I had been using Top; for the GC version, rsize wound up more than 
double the manual collection, while vsize was up about .4GB (vsize 
didn't budge using manual collection).  I'm partway through rewriting 
things to thread, so i'm not really in a position to go back and make 
a comparison using heap.

JT