Order-to-cancel ratio is a real limit and it can get you throttled

Venues care about how many orders you cancel relative to how many you actually execute, and some enforce it. I had never thought about the ratio as something worth watching until it came up in a discussion about throttling, and then I looked at my own numbers. Mine were bad. A strategy that repriced a resting order every few seconds was generating an enormous number of cancels for very few fills. Nothing had gone wrong yet — but venues do care about this, and the failure mode is being throttled or warned rather than getting a clean error. Two things I changed. I stopped repricing on every tick and started repricing only when the price had moved past a threshold. And I now log cancels and fills as a ratio so I can see it trending rather than discovering it in an email. If you run any kind of resting-order strategy, go count yours. It's a number you almost certainly have and have never looked at.