title: Core Data: Interrupt executing NSFetchRequest
body: <p>Been searching high and low for this:</p>
  
  <p>In Core Data, is there a way to interrupt/stop/cancel and executing NSFetchRequest?</p>
  
  <p>I'm implementing an incremental search in an iPhone app, and I've tried every way of optimizing it, but it's not enough (I have 42,000 records), so I have to run it in an NSOperation. When a new character is typed, I need to cancel the previous fetchRequest, but [nsoperation cancel] does nothing. </p>
  
  <p>Another approach might be to move the field I'm searching on into some other interruptible index, maybe in memory, or maybe a separate sqlite3 database, which appears to be interruptible with sqlite_interrupt.</p>