Caching NSDictionary to the local device in Objective C [duplicate]

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I am currently building an app that needs to save multiple NSDictionaries for up to 24 hours at a time. Currently I am saving these as an NSArray in NSUserDefaults. However, there eventually comes a point where there are too many NSDictionaries in the array and the app becomes slow when adding or searching for specific dictionaries in the array. I know I need to make this more efficient (and faster) but am not sure which way to go. I looked briefly into SQLite databases but it got kind of confusing when accessing tables at the same time (sometimes the databases would be locked and unable to process). Any help would be greatly appreciated!