Optimism (Optimistic Rollups) is a layer2 that aims to increase the scalability of Ethereum up to 100 times.
Everyone is waiting for Ethereum 2.0 and sharding that should improve scalability. The problem is that Ethereum, without improvements, would reach Ethereum 2.0 having lost the interest of the market.
Now any transaction on Ethereum must be individually authorized by the nodes. This slows down the network and makes it expensive. The solution is to create external blockchains (sidechains) to the main blockchain, with the aim of processing a part of the transactions and then re-transmitting them en masse to the main blockchain.
Several dApps (including Synthethix, Uniswap and dYdX) have been using this update for some time. According to Buterin, there will be an improvement of up to 105x for a simple ETH trade, up to 428x for more complex trades (such as a trade on Uniswap).
Generally speaking, sidechain creation has three main problems:
1) Increased complexity
2) There are more bugs because it is less tested
3) Greater centralization
For further information: Layer2 (Scaling)
To configure Optimism on Metamask:
Network Name: Optimistic Ethereum
New RPC URL: https://mainnet.optimism.io
Chain ID: 10
Currency Symbol: ETH
Block Explorer URL: https://optimistic.etherscan.io
Here you can find the bridge: Optimism
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