70 lines
2.5 KiB
Markdown
70 lines
2.5 KiB
Markdown
# Block syncing
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This folder holds all modules related to block syncing
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Block syncing uses ETH2 RPC protocol.
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Reference diagram
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## Eth2 RPC in
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Blocks are requested during sync by the SyncManager.
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Blocks are received by batch:
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- `syncStep(SyncManager, index, peer)`
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- in case of success:
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- `push(SyncQueue, SyncRequest, seq[SignedBeaconBlock]) is called to handle a successful sync step.
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It calls `validate(SyncQueue, SignedBeaconBlock)` on each block retrieved one-by-one
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- `validate` only enqueues the block in the SharedBlockQueue `AsyncQueue[BlockEntry]` but does no extra validation only the GossipSub case
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- in case of failure:
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- `push(SyncQueue, SyncRequest)` is called to reschedule the sync request.
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Every second when sync is not in progress, the beacon node will ask the RequestManager to download all missing blocks currently in quarantaine.
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- via `handleMissingBlocks`
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- which calls `fetchAncestorBlocks`
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- which asynchronously enqueue the request in the SharedBlockQueue `AsyncQueue[BlockEntry]`.
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The RequestManager runs an event loop:
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- that calls `fetchAncestorBlocksFromNetwork`
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- which RPC calls peers with `beaconBlocksByRoot`
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- and calls `validate(RequestManager, SignedBeaconBlock)` on each block retrieved one-by-one
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- `validate` only enqueues the block in the `AsyncQueue[BlockEntry]` but does no extra validation only the GossipSub case
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## Weak subjectivity sync
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Not implemented!
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## Comments
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The `validate` procedure name for `SyncManager` and `RequestManager`
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as no P2P validation actually occurs.
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## Sync vs Steady State
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During sync:
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- The RequestManager is deactivated
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- The syncManager is working full speed ahead
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- Gossip is deactivated
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## Bottlenecks during sync
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During sync:
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- The bottleneck is clearing the SharedBlockQueue `AsyncQueue[BlockEntry]` via `storeBlock`
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which requires full verification (state transition + cryptography)
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## Backpressure
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The SyncManager handles backpressure by ensuring that
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`current_queue_slot <= request.slot <= current_queue_slot + sq.queueSize * sq.chunkSize`.
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- queueSize is -1, unbounded, by default according to comment but all init paths uses 1 (?)
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- chunkSize is SLOTS_PER_EPOCH = 32
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However the shared `AsyncQueue[BlockEntry]` itself is unbounded.
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Concretely:
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- The shared `AsyncQueue[BlockEntry]` is bounded for sync
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- The shared `AsyncQueue[BlockEntry]` is unbounded for validated gossip blocks
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RequestManager and Gossip are deactivated during sync and so do not contribute to pressure.
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