Go-ethereum: Ask a question about the code in func SetHead

Created on 31 Oct 2019 · 4Comments · Source: ethereum/go-ethereum

func (bc *BlockChain) SetHead(head uint64) error {
    log.Warn("Rewinding blockchain", "target", head)

    bc.chainmu.Lock()
    defer bc.chainmu.Unlock()

    updateFn := func(db ethdb.KeyValueWriter, header *types.Header) {
        // Rewind the block chain, ensuring we don't end up with a stateless head block
        if currentBlock := bc.CurrentBlock(); currentBlock != nil && header.Number.Uint64() < currentBlock.NumberU64() {
            newHeadBlock := bc.GetBlock(header.Hash(), header.Number.Uint64())
            if newHeadBlock == nil {
                newHeadBlock = bc.genesisBlock
            } else {
                if _, err := state.New(newHeadBlock.Root(), bc.stateCache); err != nil {
                    // Rewound state missing, rolled back to before pivot, reset to genesis
                    newHeadBlock = bc.genesisBlock
                }
            }
            rawdb.WriteHeadBlockHash(db, newHeadBlock.Hash())
            bc.currentBlock.Store(newHeadBlock)
            headBlockGauge.Update(int64(newHeadBlock.NumberU64()))
        }
...

I want to ask, why here not try to repair the chain (call the func repair)?. Just reset to genesisBlock?

backlog bug

Source

james-ray

👍1

All 4 comments

This is a valid issue. The code originates form before we had (in-memory) state pruning, so a missing state meant fast sync + pre-sync reset. Now, with pruning, it can indeed just happen that the state is missing for this particular block, but not for some previous ones.