That was the opening statement of Vitalik Buterin, Ethereum’s inventor, at BeyondBlock in Taipei where he laid out a plan to reach Visa levels scalability within the next 3-5 years. Having two out of three is easy he says, providing examples of current solutions that have made that two out of three trade-off: Existing blockchains, like Ethereum and Bitcoin in their current state, sacrifice scalability, he says, while super big blocks, at the size of 10GB, would sacrifice decentralization, Buterin says.
One such way is through second layer solutions, like Plasma, Raiden, or the Lightning Network, however ethereum also aims to achieve the trilemma of decentralization, safety and scalability, all on-chain. “The way I generally describe sharding is… you can think of it as, in a fairly simple version, creating a blockchain where you have, lets say, a hundred different universes and each of these universes is a different account space,” Buterin says before adding: “So you can have an account in some universe or you can have a contract in some universe and you can send a transaction in some universe and if you send a transaction in some universe it only affects stuff in some universe.
Let’s imagine we keep the main blockchain and into the main blockchain we would publish a contract, and this contract would be called the validator manager contract [which] would maintain an internal Proof of Stake (PoS) system… The validator manager contract also keeps track of a set of shards… the 100 universes. A collation is basically just a group of transactions and the collation would have a collation header that would be basically a PoS signed block header, and these collation headers would be pushed into the validator manager contract, but all of the actual transactions in the shards, all of the shards states, all of the shards collations, that would go off-chain.
The only thing that goes on-chain is these collation headers and the validator manager contract would keep track of these headers and would keep track of the state roots of each shard. And this new world with its own rules which has quadratic scalability as nodes validate certain shards and act as light clients for other shards, with this new world potentially having even higher levels of scalability dependent on how sharding is implemented or incrementally improved.
http://www.trustnodes.com/2017/11/25/vitalik-buterin-lays-roadmap-ethereum-visa-levels-quadratic-sharding