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Database Layer

Erigon uses a temporal database architecture separating hot (mutable) from cold (immutable) data.

Storage Architecture

datadir/
├── chaindata/     # Hot state (MDBX) - recent blocks and state
└── snapshots/
    ├── domain/    # Latest state values
    ├── history/   # Historical value changes
    ├── idx/       # Inverted indices for search
    └── accessor/  # Additional lookup indices

Key Components

MDBX (kv/mdbx/)

  • Fork of LMDB optimized for Erigon's access patterns
  • Hot database for recent, mutable state
  • Tables defined in kv/tables.go

Temporal Database (kv/temporal/)

  • kv_temporal.go - TemporalDB wraps MDBX + Aggregator
  • Enables time-travel queries via GetAsOf(txNum)
  • Methods: GetLatest(), HistorySeek(), RangeAsOf(), IndexRange()

State Aggregator (state/)

  • aggregator.go - Central hub managing domains and indices
  • domain.go - State domain with embedded history
  • history.go - Historical value tracking
  • inverted_index.go - Time-travel indices (key → [txNums])

Four Domains

Domain Purpose Content
AccountsDomain Account state nonce, balance, code hash
StorageDomain Contract storage key-value slots
CodeDomain Contract bytecode deployed code
CommitmentDomain Merkle proofs state root commitments

Each domain manages:

  • Current values (hot, in MDBX)
  • Historical snapshots (.seg files)
  • Indices for lookups

ETL Framework (etl/)

Sorts data before database insertion to reduce write amplification:

  1. Collect changes in memory/temp files
  2. Sort by key
  3. Batch insert in order

Snapshots (seg/, downloader/)

  • .seg files store immutable historical data
  • Downloaded via BitTorrent with WebSeed fallback
  • Piece size: 2MB default
  • Verification on download

Data Flow

  1. New state changes → hot MDBX tables
  2. ETL sorts before insertion
  3. Periodic snapshots freeze old data
  4. Cold data compressed for long-term storage