Ok, lets start from basics, google's 'define: rollup' in finance is:
denoting an investment fund in which returns are reinvested and tax liabilities can be reduced.
So, in Ethereum Kingdom,
we have this below eco-system going on, an excerpt from Karl Floresch 2019 slides:
PS1: In above image, miners can earn NOT ONLY from block rewards, transaction fees, front-running (not many are aware of it but there are few groups effectively doing it), slow market arbitrage (simultaneously buying and selling same quantity of some entity at different exchange to take advantage of price difference), BUT ALSO from speed-up or cancel transaction service as some transaction seem to stuck forever as done by https://cancel-ethereum-transactions.web.app/)
PS2: Pardon me if above image does not relate well to ZK-rollup and optimistic rollup context but I intuite so.
Zero.Knowledge- Rollup is about the options being developed for layer 2 construction that increases scalability through mass transfer processing rolled into a single transaction. Where Plasma creates one transaction per transfer, ZK-Rollups bundle hundreds of transfers into a single transaction.
But communities more love Optimistic Rollup as it is also a layer 2 technology which scales Ethereum smart contracts and DApps up to 100 – 2000 transactions per second (TPS). ... Sidechain users and operators maintain the sidechain and ensure valid state transitions are committed to the mainnet contract
as full details can be found in https://ethgasstation.info/blog/what-is-optimistic-rollup-ethereums-latest-layer-2-scaling-solution/
So, latest developments in optimistic rollup have been Optimistic Virtual Machine = [OVM] (https://optimism.io/)and now, [synthetix assets can directly be staked in OVM testnet] (https://blog.synthetix.io/second-ovm-l2-testnet-snx-distribution/)
