My question is similar to this one.

Background

I'm creating a large number of objects in a core data store using NSOperations to speed things up.

I've followed all the Core Data multithreading rules - I've got a single persistent store coordinator and a managed object context per thread that on save is merging back to the main managed object context.

The Problem

When the number of threads running at once is more than 1, I get the exception logged on save of my core data store:

NSExceptionHandler has recorded the following exception:
NSInternalInconsistencyException -- optimistic locking failure

What I've Tried

My code that creates new entities is quite complex - it makes entities that have relationships with other entities that could be being created in a separate thread.

If I replace my object creation routine with some very simple code just making non-related entries, everything works perfectly.

Initially, as well as the exceptions, I was getting a save error saying core data couldn't save due to the merge failing.

I read the docs and realised I needed a merge policy on the Managed Object Context I was saving to. I set this up and as this question states, the save error goes away, but the exception remains.

My Question

Do I need to worry about these exceptions? If I do need to get rid of the exceptions, any ideas on how I do it?