Optimistic mining tip (slow block propagation)

The discussion around the challenges miners face due to slow block propagation has been a topic of considerable interest within the cryptocurrency community, as highlighted in various forums including a detailed conversation on BitcoinOps. The focus often shifts towards the delays caused by compact block propagation and transaction filtering, but an alternative aspect worth exploring is the concept of optimistic mining. This approach involves miners starting to mine on a new chain tip while its validation is still pending, a strategy that could potentially mitigate some of the issues related to slow block propagation.

The process begins when a miner receives a new (compact) block from a peer, which then undergoes several phases before being accepted as the new chain tip. Initially, the block's header is validated to ensure its hash and proof of work are correct. If any transactions are missing, the miner requests these from peers, which can introduce delays. Following this, all transactions within the block are validated, and if everything checks out, the block is accepted as the new chain tip.

The proposal suggests a modification to this process where, after the header validation, the block is placed in a special slot designated for blocks that are optimistically accepted pending validation, referred to here as the "optimistic tip." Mining template generation would then consider this optimistic tip, allowing mining efforts to proceed on the assumption that the block will eventually be validated successfully. Should the block pass validation, it takes its place as the normal chain tip, and operations continue as usual. However, if the block fails validation or if validation does not conclude within a specified timeframe (e.g., 20 seconds), the optimistic tip is cleared, and the miner reverts to the previous chain tip.

This method aims to reduce the occurrence of orphan blocks by allowing miners to continue their work without waiting for full validation, thus potentially increasing efficiency. The risk associated with this approach is considered minimal since block headers provide a layer of security against the mining of invalid blocks. This optimism-based strategy underscores a proactive solution to enhance mining operations despite inherent delays in block propagation, suggesting a balance between operational efficiency and the safeguarding measures inherent in blockchain validation protocols.