NSPersistentStoreRemoteChangeNotification with no NSPersistentHistoryTokenKey

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Created Oct ’22

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I'm processing history as presented in Synchronizing a local store to the cloud but I'm puzzled by some NSPersistentStoreRemoteChangeNotification that don't have any NSPersistentHistoryTokenKey ("historyToken").

Several notifications are emitted (launching the app is enough to get them reliably), and the userInfo only has the NSStoreUUID and storeURL, but no historyToken.

My app performs background operations that need to be canceled if there is new history to be processed, but these empty notifications means that they are canceled/resumed for nothing.

Here's what's happening in the logs before the post

CoreData: sql: BEGIN TRANSACTION
CoreData: annotation: connection 0x14a05e350 adopting snapshot:
  ss value: {length = 48, bytes = 0x18e22d00 00000000 02000000 01000010 ... ce67e038 c22b1d42 }
  pointer value:_PFSQLiteSnapshotWrapper (0x14a38ffa0) : {length = 48, bytes = 0x18e22d00 00000000 02000000 01000010 ... ce67e038 c22b1d42 }
  pointer: 0x14a390020
CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZBOOLVALUENUM, t0.ZDATEVALUE, t0.ZINTEGERVALUE, t0.ZKEY, t0.ZSTRINGVALUE, t0.ZTRANSFORMEDVALUE FROM ANSCKMETADATAENTRY t0 WHERE  t0.ZKEY IN  (?)  
CoreData: annotation: sql connection fetch time: 0.0002s
CoreData: annotation: total fetch execution time: 0.0004s for 1 rows.
CoreData: sql: COMMIT
CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZBOOLVALUENUM, t0.ZDATEVALUE, t0.ZINTEGERVALUE, t0.ZKEY, t0.ZSTRINGVALUE, t0.ZTRANSFORMEDVALUE FROM ANSCKMETADATAENTRY t0 WHERE  t0.Z_PK = ? 

CoreData: annotation: sql connection fetch time: 0.0002s
CoreData: annotation: total fetch execution time: 0.0004s for 1 rows.
CoreData: annotation: fault fulfilled from database for : 0x87dcfb0ae3b5ee85 <x-coredata://18A3AE76-9F1F-4153-8410-F15A01AED530/NSCKMetadataEntry/p2>
CoreData: sql: BEGIN EXCLUSIVE
CoreData: sql: UPDATE OR FAIL ANSCKMETADATAENTRY SET Z_OPT = ?  WHERE Z_PK = ? AND Z_OPT = ?
CoreData: sql: COMMIT
CoreData: sql: BEGIN TRANSACTION
CoreData: annotation: connection 0x14a05e350 created snapshot:
  ss {length = 48, bytes = 0x18e22d00 00000000 03000000 01000010 ... 5708fa9b fd63878d } value: 
  pointer value:{length = 8, bytes = 0x6019394a01000000}
  pointer: 0x14a391960
CoreData: sql: ROLLBACK
CoreData: debug: Remote Change Notification - Posting for com.apple.coredata.NSPersistentStoreRemoteChangeNotification.remotenotification.18A3AE76-9F1F-4153-8410-F15A01AED530
CoreData: debug: Remote Change Notification - observer received for  18A3AE76-9F1F-4153-8410-F15A01AED530 with state 0
CoreData: sql: SELECT MAX(Z_PK) FROM ATRANSACTION
CoreData: debug: Remote Change Notification - PSC to post notification for store  18A3AE76-9F1F-4153-8410-F15A01AED530 with transaction ID 0
CoreData: sql: BEGIN TRANSACTION
CoreData: annotation: connection 0x14a05e350 adopting snapshot:
  ss value: {length = 48, bytes = 0x18e22d00 00000000 03000000 01000010 ... 5708fa9b fd63878d }
  pointer value:_PFSQLiteSnapshotWrapper (0x14a3926f0) : {length = 48, bytes = 0x18e22d00 00000000 03000000 01000010 ... 5708fa9b fd63878d }
  pointer: 0x14a391960
CoreData: debug: Remote Change Notification - posting for store  18A3AE76-9F1F-4153-8410-F15A01AED530 with userInfo

Adding a guard clause to skip history processing when the NSPersistentHistoryTokenKey is missing seems fine, but I'd rather make sure this is a safe thing to do, and for that I'd like to understand why these "empty" notifications happen and what their purpose is.

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