How to know when to use fit_generator() in keras when training data gets too big for fit()?

Question

When using keras for machine learning, model.fit() is used when training data is small. When training data is too big, model.fit_generator() is recommended instead of model.fit(). How does one know when data size has become too large?

Answer 1

The moment you run into memory errors when trying to take the training data into memory, you'll have to switch to fit_generator(). There is extra overhead associated with generating data on the fly (and reading from disk to do so), so training a model on a dataset that lives in memory will always be faster.