Block Size

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"Under a Proof-of-Work consensus protocol, transactions are grouped into blocks before being verified and added to the blockchain. While every block changes the state of the ledger, the size of a block determines how much information or how many changes are included at one time. Having a smaller block size results in a more condensed and easier-to-manage network, but limits the number and speed of transactions. Having a larger block size allows for more transactions per block, but can potentially overload the system with too much data. Disagreements in ideal block size limits have been contentious in several blockchain communities. For example: disagreement over Bitcoin’s block size in 2017 eventually led to the hard fork that produced Bitcoin Cash."

Different Implementations

  • The maximum block size is typically defined in MB. Some blockchains, notably Ethereum, use a different metric; gas.
  • Some blockchains have fixed sizes, like the Bitcoin Core protocol, that limits blocks to 1 MB in size (9-2019). Each block contains at most some 4,000 transactions. Blocks are added to the blockchain on average every 10 minutes, therefore the transaction rate is limited to some 7 transactions per second (TPS).
  • Other coins have bigger blocks, like Dash with 2 MB, Bitcoin Cash with 32 MB.
  • Some blockchains have adaptable block sizes, for instance Cypherium.

The Block Size Debate

  • In the Bitcoin community there has been a long debate of multiple years about how to deal with the block size. This debate is dubbed: The Block Size Debate.
  • However not only in BTC there are debates around block size. In Ethereum there is also discussion around it:

"In order to prevent network congestion, miners on the ethereum network have recently responded to the surge in transaction activity by increasing ethereum’s “gas limit.”

Stepping back, the cost to send a transaction on the ethereum network is called gas and paid in fractions of ETH called gwei. For every block processed on the ethereum blockchain, there is a limit to the overall amount of gas that can be collected by miners.

In short, a higher gas limit means that a higher number of transactions can be included in a block. On Sept. 19, ethereum miners collectively raised network gas limits from 8 million to 10 million gwei. Ethereum blocks are now effectively 25 percent larger – allowing for larger transaction processing loads.

At the same time, the concern around larger block sizes on ethereum is that block propagation speed may slow down. The slower it is for a block to be propagated and accepted by all miners in the ethereum network, the higher the likelihood is for temporary chain splits to occur.

“As gas limit goes up, block size will eventually follow it, requiring more storage and initial sync time for nodes,” said Eric Conner, founder of ethereum information site ETHHub. “So far though, block size hasn’t really gone up despite the gas limit increasing.”

Even so, some outside of the ethereum community have viewed the collective decision-making of miners on the platform with derision.

“It’s official! Ethereum miners have unilaterally increased the gas limit and made it even harder to sync a full node,” tweeted self-proclaimed bitcoin maximalist Conner Brown. “Meanwhile ethereans rejoice at how easy it was for miners to do this without public debate.”

"EIP-1559 is the Ethereum community’s attempt to sidestep a potentially contentious debate about block size with its proposal to utilize flexible block sizes instead of fixed block sizes. By having a two-tiered system that uses a base fee and tips, EIP-1559 creates dynamic and adjustable block sizes that expand and contract depending on demand, which is defined through a system of base fees and tips."