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By design, Core Data does not issue a VACUUM SQL command to its SQLite database(s), as detailed here. I'm creating a Core Data application that'll store, and later delete, large binary files (2-10MB in size) in a SQLite db. Over time this will lead to fragmentation and a larger-than-necessary SQLite database. I'd like to periodically issue a VACUUM command, say, during a cleanup operation I run.
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The VACUUM command works by copying the contents of the database into a temporary database file and then overwriting the original with the contents of the temporary file. When overwriting the original, a rollback journal or write-ahead log WAL file is used just as it would be for any other database transaction.
The most important difference between Core Data and SQLite is that SQLite is a database while Core Data is not. That is the most important difference because there is very little to compare. Core Data and SQLite are solutions to different problems.
Yes, there is always a SQLite behind it. You can find it in the documents folder. As with every new build a new documents folder is created on the simulator it's getting quite cumbersome to search it manually everytime. Create a function in your app and print it out.
Core Data is heavily optimized with regards to caching, lazy-loading and memory management. If you use it (with the SQLite store type), especially in conjunction with NSFetchedResultsController, you should get better performance than you could get with SQLite on your own.
The supported way to do this, on OS X 10.6 / iOS 3.0 and later, is to set the NSSQLiteManualVacuumOption in the options when you are adding the store to the persistent store coordinator.
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Yes, vacuum is a recognized SQL statement in SQLite. It can be used as a normal query, or so it says.
Beware, though, as it can lead to excessive file system reads and writes—the bottleneck of practically any system—not to mention server file system fragmentation on Windows servers.
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