Request based PoV distribution (#2640)

* 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.

polkadot/node/network/protocol/src/request_response/mod.rs

@@ -60,6 +60,8 @@ pub enum Protocol {
 	ChunkFetching,
 	/// Protocol for fetching collations from collators.
 	CollationFetching,
+	/// Protocol for fetching seconded PoVs from validators of the same group.
+	PoVFetching,
 	/// Protocol for fetching available data.
 	AvailableDataFetching,
 }
@@ -107,11 +109,18 @@ impl Protocol {
 				request_timeout: DEFAULT_REQUEST_TIMEOUT_CONNECTED,
 				inbound_queue: Some(tx),
 			},
+			Protocol::PoVFetching => RequestResponseConfig {
+				name: p_name,
+				max_request_size: 1_000,
+				max_response_size: MAX_COMPRESSED_POV_SIZE as u64,
+				request_timeout: DEFAULT_REQUEST_TIMEOUT_CONNECTED,
+				inbound_queue: Some(tx),
+			},
 			Protocol::AvailableDataFetching => RequestResponseConfig {
 				name: p_name,
 				max_request_size: 1_000,
 				// Available data size is dominated by the PoV size.
-				max_response_size: 30_000_000,
+				max_response_size: MAX_COMPRESSED_POV_SIZE as u64,
 				request_timeout: DEFAULT_REQUEST_TIMEOUT,
 				inbound_queue: Some(tx),
 			},
@@ -130,6 +139,8 @@ impl Protocol {
 			Protocol::ChunkFetching => 100,
 			// 10 seems reasonable, considering group sizes of max 10 validators.
 			Protocol::CollationFetching => 10,
+			// 10 seems reasonable, considering group sizes of max 10 validators.
+			Protocol::PoVFetching => 10,
 			// Validators are constantly self-selecting to request available data which may lead
 			// to constant load and occasional burstiness.
 			Protocol::AvailableDataFetching => 100,
@@ -146,6 +157,7 @@ impl Protocol {
 		match self {
 			Protocol::ChunkFetching => "/polkadot/req_chunk/1",
 			Protocol::CollationFetching => "/polkadot/req_collation/1",
+			Protocol::PoVFetching => "/polkadot/req_pov/1",
 			Protocol::AvailableDataFetching => "/polkadot/req_available_data/1",
 		}
 	}