Add asynchronous backing guide (#788)

brunopgalvao · Copilot · nhussein11 · web-flow · commit bc21dadeb4a7 · 2025-07-29T22:32:19.000-03:00
* Add async backing guide

* python3 scripts/generate_llms.py

* formatting

* Update develop/parachains/maintenance/asynchronous-backing.md

Co-authored-by: Copilot &lt;175728472+Copilot@users.noreply.github.com&gt;

* Update develop/parachains/maintenance/asynchronous-backing.md

Co-authored-by: Nicolás Hussein &lt;80422357+nhussein11@users.noreply.github.com&gt;

* Update develop/parachains/maintenance/asynchronous-backing.md

Co-authored-by: Nicolás Hussein &lt;80422357+nhussein11@users.noreply.github.com&gt;

* Update develop/parachains/maintenance/asynchronous-backing.md

Co-authored-by: Nicolás Hussein &lt;80422357+nhussein11@users.noreply.github.com&gt;

* Update develop/parachains/maintenance/asynchronous-backing.md

Co-authored-by: Nicolás Hussein &lt;80422357+nhussein11@users.noreply.github.com&gt;

* formatting text

* formatting line breaks

* reference Polkadot Rust Docs and Polkadot SDK

* scheduling_lookahead is now lookahead and is set to 3 not 2 on Polkadot

* add content; rename page; formatting

* Update develop/parachains/maintenance/configure-asynchronous-backing.md

Co-authored-by: Nicolás Hussein &lt;80422357+nhussein11@users.noreply.github.com&gt;

* Update develop/parachains/maintenance/configure-asynchronous-backing.md

Co-authored-by: Nicolás Hussein &lt;80422357+nhussein11@users.noreply.github.com&gt;

* Update develop/parachains/maintenance/configure-asynchronous-backing.md

Co-authored-by: Nicolás Hussein &lt;80422357+nhussein11@users.noreply.github.com&gt;

* Update develop/parachains/maintenance/configure-asynchronous-backing.md

Co-authored-by: Nicolás Hussein &lt;80422357+nhussein11@users.noreply.github.com&gt;

* formatting

* formatting

* Update develop/parachains/maintenance/configure-asynchronous-backing.md

Co-authored-by: Nicolás Hussein &lt;80422357+nhussein11@users.noreply.github.com&gt;

* Update develop/parachains/maintenance/configure-asynchronous-backing.md

Co-authored-by: Nicolás Hussein &lt;80422357+nhussein11@users.noreply.github.com&gt;

* update formatting

* Update develop/parachains/maintenance/configure-asynchronous-backing.md

Co-authored-by: Dawn Kelly &lt;83190195+dawnkelly09@users.noreply.github.com&gt;

* Update develop/parachains/maintenance/configure-asynchronous-backing.md

Co-authored-by: Dawn Kelly &lt;83190195+dawnkelly09@users.noreply.github.com&gt;

* Update develop/parachains/maintenance/configure-asynchronous-backing.md

Co-authored-by: Dawn Kelly &lt;83190195+dawnkelly09@users.noreply.github.com&gt;

* Update develop/parachains/maintenance/configure-asynchronous-backing.md

Co-authored-by: Dawn Kelly &lt;83190195+dawnkelly09@users.noreply.github.com&gt;

* Update develop/parachains/maintenance/configure-asynchronous-backing.md

Co-authored-by: Dawn Kelly &lt;83190195+dawnkelly09@users.noreply.github.com&gt;

* Update develop/parachains/maintenance/configure-asynchronous-backing.md

Co-authored-by: Dawn Kelly &lt;83190195+dawnkelly09@users.noreply.github.com&gt;

* formatting updates

* use double digits for code snippets

* additional changes, updates llms

* grammarly tweaks, llms

---------

Co-authored-by: Copilot &lt;175728472+Copilot@users.noreply.github.com&gt;
Co-authored-by: Nicolás Hussein &lt;80422357+nhussein11@users.noreply.github.com&gt;
Co-authored-by: Dawn Kelly &lt;83190195+dawnkelly09@users.noreply.github.com&gt;
Co-authored-by: DAWN KELLY &lt;dawnkelly09@gmail.com&gt;
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/Cargo.toml b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/Cargo.toml
@@ -0,0 +1,3 @@
+...
+cumulus-primitives-aura = { path = "../../../../primitives/aura", default-features = false }
+...
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/apis-01.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/apis-01.rs
@@ -0,0 +1,3 @@
+fn impl_slot_duration() -> sp_consensus_aura::SlotDuration {
+    sp_consensus_aura::SlotDuration::from_millis(SLOT_DURATION)
+}
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/apis-02.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/apis-02.rs
@@ -0,0 +1,8 @@
+impl cumulus_primitives_aura::AuraUnincludedSegmentApi<Block> for Runtime {
+    fn can_build_upon(
+        included_hash: <Block as BlockT>::Hash,
+        slot: cumulus_primitives_aura::Slot,
+    ) -> bool {
+        Runtime::impl_can_build_upon(included_hash, slot)
+    }
+}
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/genesis_config_preset_snippet.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/genesis_config_preset_snippet.rs
@@ -0,0 +1,6 @@
+...
+"async_backing_params": {
+    "max_candidate_depth": 3,
+    "allowed_ancestry_len": 2
+},
+...
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-01.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-01.rs
@@ -0,0 +1,8 @@
+// Maximum number of blocks simultaneously accepted by the runtime, not yet included into the
+// relay chain.
+pub const UNINCLUDED_SEGMENT_CAPACITY: u32 = 1;
+// How many parachain blocks are processed by the relay chain per parent. Limits the number of
+// blocks authored per slot.
+pub const BLOCK_PROCESSING_VELOCITY: u32 = 1;
+// Relay chain slot duration, in milliseconds.
+pub const RELAY_chain_SLOT_DURATION_MILLIS: u32 = 6000;
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-02.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-02.rs
@@ -0,0 +1,6 @@
+// `SLOT_DURATION` is picked up by `pallet_timestamp` which is in turn picked
+// up by `pallet_aura` to implement `fn slot_duration()`.
+//
+// Change this to adjust the block time.
+pub const MILLISECS_PER_BLOCK: u64 = 12000;
+pub const SLOT_DURATION: u64 = MILLISECS_PER_BLOCK;
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-03.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-03.rs
@@ -0,0 +1,6 @@
+type ConsensusHook = cumulus_pallet_aura_ext::FixedVelocityConsensusHook<
+    Runtime,
+    RELAY_CHAIN_SLOT_DURATION_MILLIS,
+    BLOCK_PROCESSING_VELOCITY,
+    UNINCLUDED_SEGMENT_CAPACITY,
+>;
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-04.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-04.rs
@@ -0,0 +1,5 @@
+impl cumulus_pallet_parachain_system::Config for Runtime {
+    ...
+    type ConsensusHook = ConsensusHook;
+    ...
+}
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-05.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-05.rs
@@ -0,0 +1,5 @@
+impl cumulus_pallet_parachain_system::Config for Runtime {
+    ...
+    type CheckAssociatedRelayNumber = RelayNumberMonotonicallyIncreases;
+    ...
+}
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-06.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-06.rs
@@ -0,0 +1,7 @@
+impl pallet_aura::Config for Runtime {
+    ...
+    type AllowMultipleBlocksPerSlot = ConstBool<false>;
+    #[cfg(feature = "experimental")]
+    type SlotDuration = ConstU64<SLOT_DURATION>;
+    ...
+}
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-07.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-07.rs
@@ -0,0 +1,4 @@
+cumulus_pallet_parachain_system::register_validate_block! {
+    Runtime = Runtime,
+    BlockExecutor = cumulus_pallet_aura_ext::BlockExecutor::<Runtime, Executive>,
+}
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-08.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-08.rs
@@ -0,0 +1,7 @@
+impl pallet_aura::Config for Runtime {
+    type AuthorityId = AuraId;
+    type DisabledValidators = ();
+    type MaxAuthorities = ConstU32<100_000>;
+    type AllowMultipleBlocksPerSlot = ConstBool<true>;
+    type SlotDuration = ConstU64<SLOT_DURATION>;
+}
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-09.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-09.rs
@@ -0,0 +1,10 @@
+mod async_backing_params {
+    /// Maximum number of blocks simultaneously accepted by the Runtime, not yet included
+    /// into the relay chain.
+    pub(crate) const UNINCLUDED_SEGMENT_CAPACITY: u32 = 3;
+    /// How many parachain blocks are processed by the relay chain per parent. Limits the
+    /// number of blocks authored per slot.
+    pub(crate) const BLOCK_PROCESSING_VELOCITY: u32 = 1;
+    /// Relay chain slot duration, in milliseconds.
+    pub(crate) const RELAY_CHAIN_SLOT_DURATION_MILLIS: u32 = 6000;
+}
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-10.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-10.rs
@@ -0,0 +1,13 @@
+mod block_times {
+    /// This determines the average expected block time that we are targeting. Blocks will be
+    /// produced at a minimum duration defined by `SLOT_DURATION`. `SLOT_DURATION` is picked up by
+    /// `pallet_timestamp` which is in turn picked up by `pallet_aura` to implement `fn
+    /// slot_duration()`.
+    ///
+    /// Change this to adjust the block time.
+    pub const MILLI_SECS_PER_BLOCK: u64 = 6000;
+
+    // NOTE: Currently it is not possible to change the slot duration after the chain has started.
+    // Attempting to do so will brick block production.
+    pub const SLOT_DURATION: u64 = MILLI_SECS_PER_BLOCK;
+}
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-11.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-11.rs
@@ -0,0 +1,4 @@
+const MAXIMUM_BLOCK_WEIGHT: Weight = Weight::from_parts(
+    WEIGHT_REF_TIME_PER_SECOND.saturating_mul(2),
+    cumulus_primitives_core::relay_chain::MAX_POV_SIZE as u64,
+);
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-12.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/lib-12.rs
@@ -0,0 +1,5 @@
+impl pallet_timestamp::Config for Runtime {
+    ...
+    type MinimumPeriod = ConstU64<0>;
+    ...
+}
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-01.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-01.rs
@@ -0,0 +1,4 @@
+use cumulus_primitives_core::{
+    relay_chain::{CollatorPair, ValidationCode},
+    GetParachainInfo, ParaId,
+};
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-02.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-02.rs
@@ -0,0 +1,5 @@
+sc_service::spawn_tasks(sc_service::SpawnTasksParams {
+    ...
+    backend: backend.clone(),
+    ...
+})?;
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-03.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-03.rs
@@ -0,0 +1,4 @@
+fn start_consensus(
+    ...
+    backend: Arc<ParachainBackend>,
+    ...
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-04.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-04.rs
@@ -0,0 +1,7 @@
+if validator {
+    start_consensus(
+        ...
+        backend.clone(),
+        ...
+    )?;
+}
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-05.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-05.rs
@@ -0,0 +1 @@
+use cumulus_client_consensus_aura::collators::lookahead::{self as aura, Params as AuraParams};
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-06.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-06.rs
@@ -0,0 +1,12 @@
+let params = AuraParams {
+    ...
+    para_client: client.clone(),
+    para_backend: backend.clone(),
+    ...
+    code_hash_provider: move |block_hash| {
+        client.code_at(block_hash).ok().map(|c| ValidationCode::from(c).hash())
+    },
+    ...
+    authoring_duration: Duration::from_millis(2000),
+    ...
+};
diff --git a/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-07.rs b/.snippets/code/develop/parachains/maintenance/configure-asynchronous-backing/service-07.rs
@@ -0,0 +1,4 @@
+let fut = aura::run::<Block, sp_consensus_aura::sr25519::AuthorityPair, _, _, _, _, _, _, _, _>(
+    params,
+);
+task_manager.spawn_essential_handle().spawn("aura", None, fut);
diff --git a/develop/parachains/maintenance/.nav.yml b/develop/parachains/maintenance/.nav.yml
@@ -6,3 +6,4 @@ nav:
   # - 'Debug Production Issues': debug-prod-issues.md
   - 'Runtime Metrics and Monitoring': runtime-metrics-monitoring.md
   - 'Unlock Parachain': unlock-parachain.md
+  - 'Configure Asynchronous Backing': configure-asynchronous-backing.md
diff --git a/develop/parachains/maintenance/configure-asynchronous-backing.md b/develop/parachains/maintenance/configure-asynchronous-backing.md
diff --git a/llms.txt b/llms.txt

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+...`
	`2`	`+cumulus-primitives-aura = { path = "../../../../primitives/aura", default-features = false }`
	`3`	`+...`
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+fn impl_slot_duration() -> sp_consensus_aura::SlotDuration {`
	`2`	`+ sp_consensus_aura::SlotDuration::from_millis(SLOT_DURATION)`
	`3`	`+}`
-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +impl cumulus_pallet_parachain_system::Config for Runtime {
 +    ...
 +    type ConsensusHook = ConsensusHook;
 +    ...
 +}