> I don't understand why you need training on your code base to design a cache format

Because anyone willing to come in just to design your cache format is going to expect payment that is many multiples more than the engineers you already cannot afford? Long-term employees cost less, which brings them closer to being affordable, but you have to be able to keep them busy for long periods of time to realize that reduction in cost. A engineer who doesn't understand your codebase isn't going to be useful for very long.

You explained why it's beneficial for other workloads, but the original point was about this specific design