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Comment by skywhopper | Hacker News Reader

I'm going to guess that AWS is slightly more sophisticated than this, and has good data showing that the vast majority of users of this sort of instance type basically sit idle all the time. Certain customers may consistently max out their t3 instances, but those instances would be spread across thousands of host boxes, sharing resources with the tens of thousands of other customers who aren't utilizing the full capacity.

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That rarely works in reality.

Lots of instances will all burst at the same time, for example when someone has thousands of T3 instances and then dumps a bunch of work into a work scheduling system, or when debians cron kicks in at exactly midnight.

I'd much rather Amazon say "You have X% guaranteed CPU, and up to Y% extra cpu you can use on a best effort basis" I'd like to see the same for memory and disk too.

For those who need fixed performance, there should be a setting to disable that best effort extra bit.

The modern instance families support Turbo Boost, which is the X% guaranteed and up to %Y extra best effort you desire. On many of the largest instance sizes you get P-state control which lets you "disable that best effort extra bit" — but most operating systems will by default use it to strategically burst some cores even more at the expense of others.

Many workloads really just need a significant fixed amount of memory, and only periodically need high-performance CPU. T2 instances are much faster than you'd intuitively expect, if your workload is very bursty you can easily beat C4.

The newer Unlimited model "just" removes the edge case of being throttled if you run out of earned CPUCreditBalance, so you no longer have to reason about its interactions with other scaling factors.

It also allows a whole new usecase: if your workload doesn't need much memory or high I/O but will utilize as much CPU as it can get, you can save big by picking smaller burstable instances with Unlimited.

The solution if you need fixed performance is one of the other instance types, so they don't need to make it a setting on the t* types since that's not what they're for.

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