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It can go to about 10,000 transactions per second (864 million per day), in the current form. Optimizations will be needed to go beyond that.

In practice the witnesses may need to be keep it much lower than that for some time to reduce replay time, but replay time can also be improved.

Thanks @demotruk. A real credit to the Community. Stephen

Where can I learn more about tps and resource usage?

I've noticed that steemit lags during peak hours.

I'm hoping these are scaling issues with known solutions in the works.

Growth is looking insane!

I'm not sure but I believe that's just Steemit Inc not having enough Steemit.com nodes going to serve users at peak times. If so it should be just a matter of throwing up more instances.

Thanks @demotruk wonder how long it will take before that gets saturated...
say about current growth rates 4% /week (roughly) I guess that could happen in 3.6 years?