Ledger Subsystem — Technical Summary

Overview

The ledger subsystem is the core of stellar-core's state management. It orchestrates ledger closing (applying transaction sets to produce new ledger states), manages the "last closed ledger" (LCL) state, provides a transactional in-memory layer (LedgerTxn) for reading/writing ledger entries during transaction processing, maintains in-memory Soroban contract state, manages Soroban network configuration, and produces ledger close metadata for downstream consumers (e.g., Horizon).

The subsystem has a two-thread architecture: a main thread handles consensus and publishes state, while a apply thread executes transactions and commits state. The invariant LCL <= A <= Q <= H tracks ledger progress across these threads (H=heard, Q=queued, A=applying, LCL=last closed).

Key Files