Home < Bitcoin Core Dev Tech < AssumeUTXO update

AssumeUTXO update

Speakers: James O'Beirne

Date: April 27, 2023

Transcript By:

Tags: Bitcoin core, Assumeutxo

Category: Core dev tech


  • allow nodes to get a utxo set quickly (1h)
  • at the same time, no major security concessions


  • Provide serialized utxo snapshot
  • get headers chain first, load snapshot and deserialize, sync to tip from that
  • then start background verification with a 2nd snapshot
  • finally, compare hashes when background IBD hits snapshot base

Progress update

  • lots of refactoring has been done; ChainStateManager was introduced, globals removed, mempool / blockstorage refactored
  • init / shutdown logic changes have been merged
  • wallet changes done
  • p2p changes still under review (i.e. picking the chainstate to which to append new blocks )

Open issues

nFile order gets fragmented, potential problems with pruning and/or reindex -> Introduce blockfile nFile counter per chainstate types (simple change)


  • currently, pruning target w/ trailing window
  • do the same, but with two tips - different possiblities to achieve this


validationinterface signals are picked up by indices

  • could build out of order, but some indexes (coinstats) cant be build out of order

  • simple solution: just disable all indexes until sync completes

  • fancy solution: disable some indexers only

  • Introduce rpc to load chainstate

  • Put actual assumeutxo hashes into chainparams

  • In total, only ~1k loc left, although mostly in important places

Approach re-ack discussion

  • Do we really need background sync?
  • not doing the background sync is simpler, but changes security assumptions
  • Also, it would remove the necessity that every node must be able to sync the chain