Ask a question about the code in func SetHead

[james-ray]

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?

[karalabe]

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.

[james-ray]

Please allow me to fix this

[karalabe]

Sure!

[karalabe]

Fixed by #21409.