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Staged Sync

Erigon synchronizes via ordered stages. Each stage processes blocks independently and can unwind during reorgs.

Stage Pipeline Order

  1. Snapshots - Download/verify immutable historical data
  2. Headers - Download and validate block headers
  3. BlockHashes - Index blockHash → blockNumber
  4. Bodies - Download block bodies and transactions
  5. Senders - Recover transaction senders from signatures
  6. Execution - Execute blocks and compute state
  7. TxLookup - Index txHash → blockNumber
  8. Finish - Update RPC-visible head block

Key Files

  • sync.go - Sync struct orchestrates stage execution, tracks unwind points
  • stageloop/stageloop.go - StageLoop() runs continuous sync cycle
  • default_stages.go - Stage factory functions and ordering (DefaultStages(), DefaultForwardOrder, DefaultUnwindOrder)
  • stages/stages.go - SyncStage constants and progress tracking

Stage Interface

Each stage implements:

type Stage struct {
    ID      stages.SyncStage
    Forward ExecFunc   // Execute stage forward
    Unwind  UnwindFunc // Handle reorgs
    Prune   PruneFunc  // Remove old data
}

Configuration Pattern

Each stage has a config struct (e.g., HeadersCfg, ExecuteBlockCfg) containing:

  • Database handles
  • P2P handlers
  • Chain config
  • Batch sizes and tuning parameters

Reorg Handling

  1. UnwindTo() called with target block and reason
  2. Stages unwind in reverse order (DefaultUnwindOrder)
  3. State rolled back via domain writers
  4. Execution resumes from unwind point

Stage Implementations

File Stage Purpose
stage_snapshots.go Snapshots Download segment files
stage_headers.go Headers P2P header download
stage_blockhashes.go BlockHashes blockHash→blockNum index
stage_bodies.go Bodies P2P body download
stage_senders.go Senders Signature recovery
stage_execute.go Execution Block execution, state changes
stage_txlookup.go TxLookup txHash→blockNum index
stage_finish.go Finish Update head for RPC

Supporting Modules

  • headerdownload/ - Header P2P download algorithms
  • bodydownload/ - Body P2P download algorithms