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Request based PoV distribution (#2640)

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* Indentation fix.

* Prepare request-response for PoV fetching.

* Drop old PoV distribution.

* WIP: Fetch PoV directly from backing.

* Backing compiles.

* Runtime access and connection management for PoV distribution.

* Get rid of seemingly dead code.

* Implement PoV fetching.

Backing does not yet use it.

* Don't send `ConnectToValidators` for empty list.

* Even better - no need to check over and over again.

* PoV fetching implemented.

+ Typechecks
+ Should work

Missing:

- Guide
- Tests
- Do fallback fetching in case fetching from seconding validator fails.

* Check PoV hash upon reception.

* Implement retry of PoV fetching in backing.

* Avoid pointless validation spawning.

* Add jaeger span to pov requesting.

* Add back tracing.

* Review remarks.

* Whitespace.

* Whitespace again.

* Cleanup + fix tests.

* Log to log target in overseer.

* Fix more tests.

* Don't fail if group cannot be found.

* Simple test for PoV fetcher.

* Handle missing group membership better.

* Add test for retry functionality.

* Fix flaky test.

* Spaces again.

* Guide updates.

* Spaces.
This commit is contained in:
Robert Klotzner
2021-03-28 17:11:38 +02:00
committed by GitHub
parent 27b6d83974
commit c6f07d8f31
35 changed files with 1382 additions and 3184 deletions
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polkadot/roadmap/implementers-guide/src/node/backing/candidate-backing.md
+8 -8
View File
@@ -18,7 +18,7 @@ Output:
- [`RuntimeApiMessage`][RAM]
- [`CandidateSelectionMessage`][CSM]
- [`ProvisionerMessage`][PM]
- [`PoVDistributionMessage`][PDM]
- [`AvailabilityDistributionMessage`][ADM]
- [`StatementDistributionMessage`][SDM]
## Functionality
@@ -39,8 +39,11 @@ The subsystem should maintain a set of handles to Candidate Backing Jobs that ar
### On Receiving `CandidateBackingMessage`
* If the message is a [`CandidateBackingMessage`][CBM]`::GetBackedCandidates`, get all backable candidates from the statement table and send them back.
* If the message is a [`CandidateBackingMessage`][CBM]`::Second`, sign and dispatch a `Seconded` statement only if we have not seconded any other candidate and have not signed a `Valid` statement for the requested candidate. Signing both a `Seconded` and `Valid` message is a double-voting misbehavior with a heavy penalty, and this could occur if another validator has seconded the same candidate and we've received their message before the internal seconding request. After successfully dispatching the `Seconded` statement we have to distribute the PoV.
* If the message is a [`CandidateBackingMessage`][CBM]`::Statement`, count the statement to the quorum. If the statement in the message is `Seconded` and it contains a candidate that belongs to our assignment, request the corresponding `PoV` from the `PoVDistribution` and launch validation. Issue our own `Valid` or `Invalid` statement as a result.
* If the message is a [`CandidateBackingMessage`][CBM]`::Second`, sign and dispatch a `Seconded` statement only if we have not seconded any other candidate and have not signed a `Valid` statement for the requested candidate. Signing both a `Seconded` and `Valid` message is a double-voting misbehavior with a heavy penalty, and this could occur if another validator has seconded the same candidate and we've received their message before the internal seconding request.
* If the message is a [`CandidateBackingMessage`][CBM]`::Statement`, count the statement to the quorum. If the statement in the message is `Seconded` and it contains a candidate that belongs to our assignment, request the corresponding `PoV` from the backing node via `AvailabilityDistribution` and launch validation. Issue our own `Valid` or `Invalid` statement as a result.
If the seconding node did not provide us with the `PoV` we will retry fetching from other backing validators.
> big TODO: "contextual execution"
>
@@ -112,11 +115,8 @@ fn spawn_validation_work(candidate, parachain head, validation function) {
### Fetch Pov Block
Create a `(sender, receiver)` pair.
Dispatch a [`PoVDistributionMessage`][PDM]`::FetchPoV(relay_parent, candidate_hash, sender)` and listen on the receiver for a response.
Dispatch a [`AvailabilityDistributionMessage`][PDM]`::FetchPoV{ validator_index, pov_hash, candidate_hash, tx, } and listen on the passed receiver for a response. Availability distribution will send the request to the validator specified by `validator_index`, which might not be serving it for whatever reasons, therefore we need to retry with other backing validators in that case.
### Distribute Pov Block
Dispatch a [`PoVDistributionMessage`][PDM]`::DistributePoV(relay_parent, candidate_descriptor, pov)`.
### Validate PoV Block
@@ -135,7 +135,7 @@ Dispatch a [`StatementDistributionMessage`][PDM]`::Share(relay_parent, SignedFul
[CVM]: ../../types/overseer-protocol.md#validation-request-type
[PM]: ../../types/overseer-protocol.md#provisioner-message
[CBM]: ../../types/overseer-protocol.md#candidate-backing-message
[PDM]: ../../types/overseer-protocol.md#pov-distribution-message
[ADM]: ../../types/overseer-protocol.md#availability-distribution-message
[SDM]: ../../types/overseer-protocol.md#statement-distribution-message
[CS]: candidate-selection.md