Vitalik: Why I’m not worried about loose block capacity in EIP-1559

Source | notes.ethereum.org/@vbuterin

Author: Vitalik Buterin

One criticism of EIP-1559 is that the block size is variable, floating in the range of [0,25M] instead of a fixed 12.5M gas limit, which requires clients to handle double the load. This argument is further interpreted as, if we believe that clients can handle such a high load, then they should be able to handle such a high load at any time, so we might as well abandon EIP-1559 and do something more useful directly - double the block size limit.

The core idea behind this is that the primary harm of large blocks comes from the largest blocks sent by clients, not the average block size. I think this is wrong (and therefore EIP-1559 does not pose a higher risk to clients than a fixed gas limit), and here are my reasons.

➤ Review: What are the reasons for not raising the gas limit to 100M immediately?

Three reasons:

1. Normal block processing time will increase

An increase from the current ~400 ms to ~3.2s will have many negative consequences:

2. Due to DoS attacks, the block processing time will be extended in the worst case, from the current 20~80 seconds to possible 160~640 seconds.

3. Storage growth rates will increase

From about 50 GB/month now to about 400 GB/month, this will result in

Please note: everything under reasons 1 and 3 only applies to long-term normal usage, not peak usage. Therefore, if you want to consider the impact of peak usage, just focus on reason 2.

➤ Argument 1: EIP-2929 has made up for the shortcomings of EIP-1559

EIP-2929 increases the gas cost of storage access operations, which has increased the gas consumption required for the worst-case DoS attack by a factor of 3. This means that EIP-2929 combined with EIP-1559 actually reduces the gas consumption required to process blocks by 1.5 times compared to the current worst-case scenario.

A natural question here is: "If EIP-2929 is so good, why not just raise the gas limit to 25M or 37.5M?" The answer is simple: reason 2 is not the only reason to avoid increasing gas consumption. Even if the DoS problem can be completely solved, the problems under reasons 1 and 3 will still exist in the foreseeable future. Therefore, the additional slack given by EIP-2929 cannot be used to significantly increase the block capacity.

➤ Argument 2: For DoS attacks of the same magnitude, the disadvantages caused by the peak of a short-term attack are far less than those caused by a long-term attack.

If an attacker attacks the chain and fills the blocks with garbage data up to the maximum block capacity (2 times the target capacity), the gas price of each block will increase by 1.125 times. This increase is exponential: continuously generating 5 full blocks (about 65 seconds) will increase the gas price by 1.8 times, and after 5 minutes, the gas price will increase by 15 times (225 times after 10 minutes). In order to maintain the attack, the attacker must pay all transaction fees according to these crazy rising prices. Therefore, a realistic attack can last about 5 minutes.

What happens if the client receives blocks generated within these 5 minutes (each block takes 20-60 seconds to process)? Obviously, the chain processing speed will become very slow during this period. There will be many short-range forks . In fact, forks mean that the attacker can still roll back the on-chain transactions after the attack with a small amount of hash power (for example, about 20%). This is a very bad situation.

However, this is much better than an attack that the attacker can sustain for an hour or even a day. Most transactions and other services now wait for confirmation for more than 5 minutes, and only extremely vulnerable services will be disrupted because it is too difficult for them to send a transaction in 5 minutes, and rollbacks or denials of service that last for hours or even days, like the Shanghai attack in 2016, will have very serious consequences.

Therefore, a 5 minute sustained spike to 25 million gas is much less risky than a gas limit of 25 million.

➤ Argument 3: The short-term peak has already occurred

The Poisson process inherent in proof-of-work mining means that there is randomness in when blocks are published. In fact, the randomness alone causes a spike of twice the chain capacity once a week, which lasts for five minutes.

(Note: this is caused by a large number of blocks of equal capacity rather than the same number of large blocks, but as far as I know there is no evidence or reason to believe that the gas consumed by processing a single block grows superlinearly)

So, to some extent, peak usage is a known quantity and the ecosystem has been able to ignore its impact so far.

Original link: https://notes.ethereum.org/@vbuterin/eip_1559_spikes

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