A fast-path for requesting AvailableData from backing validators (#2453)

* guide changes for a fast-path requesting from backing validators * add backing group to availability recovery message * add new phase to interaction * typos * add full data messages * handle new network messages * dispatch full data requests * cleanup * check chunk index * test for invalid recovery * tests * Typos. * fix some grumbles * be more explicit about error handling and control flow * fast-path param * use with_chunks_only in Service Co-authored-by: Robert Klotzner <robert.klotzner@gmx.at>
2026-05-30 11:41:02 +00:00 · 2021-02-17 13:51:50 -06:00
parent 4a5e5f13ae
commit b7aac51341
11 changed files with 950 additions and 196 deletions
@@ -267,9 +267,9 @@ On receiving an `ApprovedAncestor(Hash, BlockNumber, response_channel)`:
  * If `RequiredTranches::Exact { next_no_show, .. } - set a wakeup for the next no-show tick.

 #### Launch Approval Work
-  * Requires `(SessionIndex, SessionInfo, CandidateReceipt, ValidatorIndex, block_hash, candidate_index)`
+  * Requires `(SessionIndex, SessionInfo, CandidateReceipt, ValidatorIndex, backing_group, block_hash, candidate_index)`
  * Extract the public key of the `ValidatorIndex` from the `SessionInfo` for the session.
-  * Issue an `AvailabilityRecoveryMessage::RecoverAvailableData(candidate, session_index, response_sender)`
+  * Issue an `AvailabilityRecoveryMessage::RecoverAvailableData(candidate, session_index, Some(backing_group), response_sender)`
  * Load the historical validation code of the parachain by dispatching a `RuntimeApiRequest::HistoricalValidationCode(`descriptor.para_id`, `descriptor.relay_parent`)` against the state of `block_hash`.
  * Spawn a background task with a clone of `background_tx`
    * Wait for the available data
@@ -1,7 +1,5 @@
 # Availability Recovery

-> TODO: <https://github.com/paritytech/polkadot/issues/1597>
-
 This subsystem is the inverse of the [Availability Distribution](availability-distribution.md) subsystem: validators will serve the availability chunks kept in the availability store to nodes who connect to them. And the subsystem will also implement the other side: the logic for nodes to connect to validators, request availability pieces, and reconstruct the `AvailableData`.

 This version of the availability recovery subsystem is based off of direct connections to validators. In order to recover any given `AvailableData`, we must recover at least `f + 1` pieces from validators of the session. Thus, we will connect to and query randomly chosen validators until we have received `f + 1` pieces.
@@ -13,7 +11,7 @@ This version of the availability recovery subsystem is based off of direct conne
 Input:

 - NetworkBridgeUpdateV1(update)
- AvailabilityRecoveryMessage::RecoverAvailableData(candidate, session, response)
+- AvailabilityRecoveryMessage::RecoverAvailableData(candidate, session, backing_group, response)

 Output:

@@ -26,13 +24,18 @@ Output:
 We hold a state which tracks the current recovery interactions we have live, as well as which request IDs correspond to which interactions. An interaction is a structure encapsulating all interaction with the network necessary to recover the available data.

 ```rust
-type ChunkResponse = Result<(PeerId, ErasureChunk), Unavailable>;
+type DataResponse<T> = Result<(PeerId, ValidatorIndex, T), Unavailable>;

-struct AwaitedChunk {
+enum Awaited {
+    Chunk(AwaitedData<ErasureChunk>),
+    FullData(AwaitedData<AvailableData>),
+}
+
+struct AwaitedData<T> {
    issued_at: Instant,
    validator_index: ValidatorIndex,
    candidate_hash: CandidateHash,
-    response: ResponseChannel<ChunkResponse>,
+    response: ResponseChannel<DataResponse<T>>,
 }

 struct State {
@@ -40,8 +43,8 @@ struct State {
    interactions: Map<CandidateHash, InteractionHandle>,
    /// A recent block hash for which state should be available.
    live_block_hash: Hash,
-    discovering_validators: Map<AuthorityDiscoveryId, Vec<AwaitedChunk>>,
-    live_chunk_requests: Map<RequestId, (PeerId, AwaitedChunk)>,
+    discovering_validators: Map<AuthorityDiscoveryId, Vec<Awaited>>,
+    live_requests: Map<RequestId, (PeerId, Awaited)>,
    next_request_id: RequestId,
    connecting_validators: Stream<(AuthorityDiscoveryId, PeerId)>,

@@ -63,12 +66,19 @@ enum FromInteraction {
    // An interaction concluded.
    Concluded(CandidateHash, Result<AvailableData, RecoveryError>),
    // Make a request of a particular chunk from a particular validator.
-    MakeRequest(
+    MakeChunkRequest(
        AuthorityDiscoveryId, 
        CandidateHash, 
        ValidatorIndex, 
-        ResponseChannel<ChunkResponse>,
+        ResponseChannel<DataResponse<ErasureChunk>>,
    ),
+    // Make a request of the full data from a particular validator.
+    MakeDataRequest(
+        AuthorityDiscoveryId,
+        CandidateHash,
+        ValidatorIndex,
+        ResponseChannel<DataResponse<AvailableData>>,
+    )
    // Report a peer.
    ReportPeer(
        PeerId,
@@ -76,19 +86,35 @@ enum FromInteraction {
    ),
 }

-struct Interaction {
-    to_state: Sender<FromInteraction>,
+struct InteractionParams {
    validator_authority_keys: Vec<AuthorityId>,
    validators: Vec<ValidatorId>,
-    // a random shuffling of the validators which indicates the order in which we connect to the validators and
-    // request the chunk from them.
-    shuffling: Vec<ValidatorIndex>, 
    // The number of pieces needed.
    threshold: usize, 
    candidate_hash: Hash,
    erasure_root: Hash,
-    received_chunks: Map<ValidatorIndex, ErasureChunk>,
-    requesting_chunks: FuturesUnordered<Receiver<ChunkResponse>>,
+}
+
+enum InteractionPhase {
+    RequestFromBackers {
+        // a random shuffling of the validators from the backing group which indicates the order
+        // in which we connect to them and request the chunk.
+        shuffled_backers: Vec<ValidatorIndex>,
+        requesting_pov: Option<Receiver<DataResponse<AvailableData>>>
+    }
+    RequestChunks {
+        // a random shuffling of the validators which indicates the order in which we connect to the validators and
+        // request the chunk from them.
+        shuffling: Vec<ValidatorIndex>, 
+        received_chunks: Map<ValidatorIndex, ErasureChunk>,
+        requesting_chunks: FuturesUnordered<Receiver<DataResponse<ErasureChunk>>>,
+    }
+}
+
+struct Interaction {
+    to_state: Sender<FromInteraction>,
+    params: InteractionParams,
+    phase: InteractionPhase,
 }
 ```

@@ -100,7 +126,7 @@ Ignore `BlockFinalized` signals.

 On `Conclude`, shut down the subsystem.

-#### `AvailabilityRecoveryMessage::RecoverAvailableData(receipt, session, response)`
+#### `AvailabilityRecoveryMessage::RecoverAvailableData(receipt, session, Option<backing_group_index>, response)`

 1. Check the `availability_lru` for the candidate and return the data if so.
 1. Check if there is already an interaction handle for the request. If so, add the response handle to it.
@@ -114,9 +140,15 @@ On `Conclude`, shut down the subsystem.
 1. Load the entry from the `interactions` map. It should always exist, if not for logic errors. Send the result to each member of `awaiting`.
 1. Add the entry to the availability_lru.

-#### `FromInteraction::MakeRequest(discovery_pub, candidate_hash, validator_index, response)`
+#### `FromInteraction::MakeChunkRequest(discovery_pub, candidate_hash, validator_index, response)`

-1. Add an `AwaitedRequest` to the `discovering_validators` map under `discovery_pub`.
+1. Add an `Awaited::Chunk` to the `discovering_validators` map under `discovery_pub`.
+1. Issue a `NetworkBridgeMessage::ConnectToValidators`.
+1. Add the stream of connected validator events to `state.connecting_validators`.
+
+#### `FromInteraction::MakeDataRequest(discovery_pub, candidate_hash, validator_index, response)`
+
+1. Add an `Awaited::FullData` to the `discovering_validators` map under `discovery_pub`.
 1. Issue a `NetworkBridgeMessage::ConnectToValidators`.
 1. Add the stream of connected validator events to `state.connecting_validators`.

@@ -129,24 +161,39 @@ On `Conclude`, shut down the subsystem.
 #### On `connecting_validators` event:

 1. If the validator exists under `discovering_validators`, remove the entry.
-1. For each `AwaitedChunk` in the entry, issue a `AvailabilityRecoveryV1Message::RequestChunk(next_request_id, candidate_hash, validator_index)` and make an entry in the `live_chunk_requests` map.
+1. For each `Awaited` in the entry, 
+  1. If `Awaited::Chunk` issue a `AvailabilityRecoveryV1Message::RequestChunk(next_request_id, candidate_hash, validator_index)` and make an entry in the `live_requests` map.
+  1. If `Awaited::FullData` issue a `AvailabilityRecoveryV1Message::RequestFullData(next_request_id, candidate_hash, validator_index)` and make an entry in the `live_requests` map.
+  1. Increment `next_request_id`.

 #### On receiving `AvailabilityRecoveryV1::RequestChunk(r_id, candidate_hash, validator_index)`

-1. Issue a `AvailabilityStore::QueryChunk(candidate-hash, validator_index, response)` message.
+1. Issue a `AvailabilityStore::QueryChunk(candidate_hash, validator_index, response)` message.
 1. Whatever the result, issue a `AvailabilityRecoveryV1Message::Chunk(r_id, response)` message.

 #### On receiving `AvailabilityRecoveryV1::Chunk(r_id, chunk)`

-1. If there exists an entry under `r_id`, remove it. If there doesn't exist one, report the peer and return. If the peer in the entry doesn't match the sending peer, reinstate the entry, report the peer, and return.
+1. If there exists an entry under `r_id`, remove it. If there doesn't exist one, report the peer and return. If the entry is not `Awaited::Chunk` or the peer in the entry doesn't match the sending peer, reinstate the entry, report the peer, and return.
 1. Send the chunk response on the `awaited_chunk` for the interaction to handle.

+#### On receiving `AvailabilityRecoveryV1::RequestFullData(r_id, candidate_hash)`
+
+1. Issue a `AvailabilityStore::QueryAvailableData(candidate_hash, response)` message.
+1. Whatever the result, issue a `AvailabilityRecoveryV1Message::FullData(r_id, response)` message.
+
+#### On receiving `AvailabilityRecoveryV1::FullData(r_id, data)`
+
+1. If there exists an entry under `r_id`, remove it. If there doesn't exist one, report the peer and return. If the entry is not `Awaited::FullData` or the peer in the entry doesn't match the sending peer, reinstate the entry, report the peer, and return.
+1. Send the data response on the `response` channel for the interaction to handle.
+
 ### Interaction logic

-#### `launch_interaction(session_index, session_info, candidate_receipt, candidate_hash)`
+#### `launch_interaction(session_index, session_info, candidate_receipt, candidate_hash, Option<backing_group_index>)`

 1. Compute the threshold from the session info. It should be `f + 1`, where `n = 3f + k`, where `k in {1, 2, 3}`, and `n` is the number of validators.
-1. Set the various fields of `Interaction` based on the validator lists in `session_info`. Compute a random shuffling of the validator indices.
+1. Set the various fields of `InteractionParams` based on the validator lists in `session_info` and information about the candidate.
+1. If the `backing_group_index` is `Some`, start in the `RequestFromBackers` phase with a shuffling of the backing group validator indices and a `None` requesting value.
+1. Otherwise, start in the `RequestChunks` phase with `received_chunks` and `requesting_chunks` both empty.
 1. Set the `to_state` sender to be equal to a clone of `state.from_interaction_tx`.
 1. Initialize `received_chunks` to an empty set, as well as `requesting_chunks`.

@@ -160,10 +207,20 @@ const N_PARALLEL: usize = 50;
 ```

 Loop:
-  * Poll for new updates from `requesting_chunks`. Check merkle proofs of any received chunks, and any failures should lead to issuance of a `FromInteraction::ReportPeer` message.
-  * If `received_chunks` has more than `threshold` entries, attempt to recover the data. If that fails, or a re-encoding of it doesn't match the expected erasure root, break and issue a `FromInteraction::Concluded(RecoveryError::Invalid)`. Otherwise, issue a `FromInteraction::Concluded(Ok(()))`.
-  * While there are fewer than `N_PARALLEL` entries in `requesting_chunks`,
-    * Pop the next item from `shuffling`. If it's empty and `requesting_chunks` is empty, break and issue a `FromInteraction::Concluded(RecoveryError::Unavailable)`.
-    * Initialize `(tx, rx)`.
-    * Issue a `FromInteraction::MakeRequest(validator, candidate_hash, validator_index, tx)`.
-    * Add `rx` to `requesting_chunks`.
+  * If the phase is `InteractionPhase::RequestFromBackers`
+    * If the `requesting_pov` is `Some`, poll for updates on it. If it concludes, set `requesting_pov` to `None`. 
+        * If it concludes with a `None` result, return to beginning. 
+        * If it concludes with available data, attempt a re-encoding. 
+            * If it has the correct erasure-root, break and issue a `Concluded(Ok(available_data))`. 
+            * If it has an incorrect erasure-root, issue a `FromInteraction::ReportPeer` message and return to beginning.
+    * If the `requesting_pov` is `None`, take the next backer off the `shuffled_backers`.
+        * If the backer is `Some`, initialize `(tx, rx)`, issue a `FromInteraction::MakeFullDataRequest(validator, candidate_hash, validator_index, tx)`, set `requesting_pov` to `Some` and return.
+        * If the backer is `None`, set the phase to `InteractionPhase::RequestChunks` with a random shuffling of validators and empty `received_chunks` and `requesting_chunks`.
+  * If the phase is `InteractionPhase::RequestChunks`:
+    * Poll for new updates from `requesting_chunks`. Check merkle proofs of any received chunks, and any failures should lead to issuance of a `FromInteraction::ReportPeer` message.
+    * If `received_chunks` has more than `threshold` entries, attempt to recover the data. If that fails, or a re-encoding produces an incorrect erasure-root, break and issue a `Concluded(RecoveryError::Invalid)`. If correct, break and issue `Concluded(Ok(available_data))`.
+    * While there are fewer than `N_PARALLEL` entries in `requesting_chunks`,
+        * Pop the next item from `shuffling`. If it's empty and `requesting_chunks` is empty, break and set the phase to `Concluded(None)`.
+        * Initialize `(tx, rx)`.
+        * Issue a `FromInteraction::MakeChunkRequest(validator, candidate_hash, validator_index, tx)`.
+        * Add `rx` to `requesting_chunks`.
@@ -58,6 +58,12 @@ enum AvailabilityRecoveryV1Message {
 	/// Respond with chunk for a given candidate hash and validator index.
 	/// The response may be `None` if the requestee does not have the chunk.
 	Chunk(RequestId, Option<ErasureChunk>),
+	/// Request the full data for a given candidate hash.
+	RequestFullData(RequestId, CandidateHash),
+	/// Respond with data for a given candidate hash and validator index.
+	/// The response may be `None` if the requestee does not have the data.
+	FullData(RequestId, Option<AvailableData>),
+
 }
 ```

@@ -160,6 +160,7 @@ enum AvailabilityRecoveryMessage {
    RecoverAvailableData(
        CandidateReceipt,
        SessionIndex,
+        Option<GroupIndex>, // Backing validator group to request the data directly from.
        ResponseChannel<Result<AvailableData, RecoveryError>>,
    ),
 }