How expensive is it to perform fetch request in Core Data?
core-data, iphone
Solution
It's relatively expensive. Each fetch you execute implies a round trip from the context through the model to the persistent store, which itself implies a file access. At best, your fetch will be as slow as the access to the store's file. In certain cases (especially fetching large binary BLOBs), it will be considerably slower. Fetch with caution.
However, remember that a fetch is not as expensive as firing a fault. You should worry more about firing faults to access data than you should doing additional fetches. Additionally, executing one or a few large fetches is considerably less expensive than running many small fetches (much like accessing one large file is easier than accessing a hundred small ones).
The best policy is to try to anticipate when designing your app what data will be necessary, then fetch it at once or in a few large fetches and cache it as long as you can.
Problem
How expensive is it to call executeFetchRequest on the managedObjectContext? Does it depend on the data set size? Is this something that can be done often or should be avoided as much as possible?