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Asked: 2026-06-06T08:33:27+00:00

I’m working with a very small sample project that can be downloaded from here

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I’m working with a very small sample project that can be downloaded from here. What I’m trying to do is debug why fetching is taking so long in my own project, but I’ve used this project as a sort of benchmark. I’ve enabled -com.apple.CoreData.SQLDebug 1in my scheme so I can see what commands are being sent to the SQLite store with my fetches.

First, in the AppDelegate, I just wrap the first part (where the bank is being created) in a for loop to create 1000 objects. Them comment out the fetch request from the AppDelegate.

Then, in the FBCFMasterViewController, there is a fetch request there. Upon running the app after saving the 1000 items, and fetching them to an NSFetchedResultsController, you’ll see thousands of output lines similar to these:

2012-06-23 09:16:30.374 FailedBankCD[90166:fb03] CoreData: annotation: sql connection fetch time: 0.0004s
2012-06-23 09:16:30.375 FailedBankCD[90166:fb03] CoreData: annotation: total fetch execution time: 0.0009s for 1 rows.
2012-06-23 09:16:30.375 FailedBankCD[90166:fb03] CoreData: annotation: fault fulfilled from database for : 0xc3e9060 <x-coredata://60E5B64A-83AB-4E6A-BEAD-5FFF50DB7F66/FailedBankDetails/p823>
2012-06-23 09:16:30.376 FailedBankCD[90166:fb03] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZCLOSEDATE, t0.ZUPDATEDATE, t0.ZZIP, t0.ZINFO FROM ZFAILEDBANKDETAILS t0 WHERE  t0.Z_PK = ?

What I’m guessing that’s from is that the sortDescriptor is initialized with key details.closeDate, which is a relationship, so as it sorts by that property, it has to fetch fault each object in, causing thousands of lines of output to appear.

So I changed the sortDescriptor to sort on the property city instead, and this time when I run, I get the following output:

2012-06-23 08:53:04.924 FailedBankCD[89564:fb03] CoreData: sql: SELECT 0, t0.Z_PK FROM ZFAILEDBANKINFO t0 ORDER BY t0.ZCITY DESC
2012-06-23 08:53:04.929 FailedBankCD[89564:fb03] CoreData: annotation: sql connection fetch time: 0.0049s
2012-06-23 08:53:04.930 FailedBankCD[89564:fb03] CoreData: annotation: total fetch execution time: 0.0059s for 1009 rows.
2012-06-23 08:53:04.936 FailedBankCD[89564:fb03] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZCITY, t0.ZNAME, t0.ZSTATE, t0.ZDETAILS FROM ZFAILEDBANKINFO t0 WHERE  t0.Z_PK IN  (?,?,?,?,?,?,?,?,?,?)  ORDER BY t0.ZCITY DESC LIMIT 10
2012-06-23 08:53:04.938 FailedBankCD[89564:fb03] CoreData: annotation: sql connection fetch time: 0.0013s
2012-06-23 08:53:04.939 FailedBankCD[89564:fb03] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZCLOSEDATE, t0.ZUPDATEDATE, t0.ZZIP, t0.ZINFO FROM ZFAILEDBANKDETAILS t0 WHERE  t0.ZINFO IN  (?,?,?,?,?,?,?,?,?,?)  
2012-06-23 08:53:04.971 FailedBankCD[89564:fb03] CoreData: annotation: sql connection fetch time: 0.0318s
2012-06-23 08:53:04.972 FailedBankCD[89564:fb03] CoreData: annotation: total fetch execution time: 0.0326s for 10 rows.
2012-06-23 08:53:04.973 FailedBankCD[89564:fb03] CoreData: annotation: Prefetching with key 'details'.  Got 10 rows.
2012-06-23 08:53:04.974 FailedBankCD[89564:fb03] CoreData: annotation: total fetch execution time: 0.0372s for 10 rows.

I don’t get repeating thousands of lines of output anymore, and this appears to be the expected output. However, if I run again, without even modifying anything, I again get thousands of lines of output similar to the following:

2012-06-23 09:19:31.263 FailedBankCD[90216:fb03] CoreData: annotation: sql connection fetch time: 0.0006s
2012-06-23 09:19:31.264 FailedBankCD[90216:fb03] CoreData: annotation: total fetch execution time: 0.0010s for 20 rows.
2012-06-23 09:19:31.264 FailedBankCD[90216:fb03] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZCITY, t0.ZNAME, t0.ZSTATE, t0.ZDETAILS FROM ZFAILEDBANKINFO t0 WHERE  t0.Z_PK IN  (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)  ORDER BY t0.ZCITY DESC LIMIT 20

This is odd behavior, no? Can anyone quickly replicate this and explain what’s going on, and why I’m getting thousands of lines of output?

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1 Answer

  1. Editorial Team

    close_date and city aren’t indexed, that’s explain the thousands of queries, and probably low performance. For the difference between runs, I would bet on the cache you are using : 

    NSFetchedResultsController *theFetchedResultsController =
[[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                    managedObjectContext:managedObjectContext sectionNameKeyPath:nil
                                               cacheName:@"Root"];
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