remove set_epoch

ultralytics/engine/trainer.py

@@ -339,7 +339,7 @@ class BaseTrainer:
             self.plot_idx.extend([base_idx, base_idx + 1, base_idx + 2])
         epoch = self.start_epoch
         self.optimizer.zero_grad()  # zero any resumed gradients to ensure stability on train start
-        self.train_loader.set_epoch(epoch)   # iterate dataloader for resuming
+        # self.train_loader.set_epoch(epoch)   # iterate dataloader for resuming, could be extremely slow for large dataset
         while True:
             self.epoch = epoch
             self.run_callbacks("on_train_epoch_start")