Add comment/TODO about method we use to copy the db file

core/lib.rs

@@ -1738,8 +1738,13 @@ impl Connection {
         self.pager.borrow().clone()
     }
 
-    /// Copy the current Database and write out to a new file
     #[cfg(feature = "fs")]
+    /// Copy the current Database and write out to a new file.
+    /// TODO: sqlite3 instead essentially does the equivalent of
+    /// `.dump` and creates a new .db file from that.
+    ///
+    /// Because we are instead making a copy of the File, as a side-effect we are
+    /// also having to checkpoint the database.
     pub fn copy_db(&self, file: &str) -> Result<()> {
         // use a new PlatformIO instance here to allow for copying in-memory databases
         let io: Arc<dyn IO> = Arc::new(PlatformIO::new()?);