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cumulus: Remove max_depth for the parent search #10973

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Merged
bkchr merged 2 commits into from
Feb 3, 2026
Merged

cumulus: Remove max_depth for the parent search #10973

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cumulus: Remove `max_depth` for the parent search
bkchr Feb 3, 2026
c998ac2
Update from github-actions[bot] running command 'prdoc --audience nod…
github-actions[bot] Feb 3, 2026
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14 changes: 0 additions & 14 deletions cumulus/client/consensus/aura/src/collators/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -43,19 +43,6 @@ pub mod basic;
pub mod lookahead;
pub mod slot_based;

// This is an arbitrary value which is guaranteed to exceed the required depth for 500ms blocks
// built with a relay parent offset of 1. It must be larger than the unincluded segment capacity.
//
// The formula we use to compute the capacity of the unincluded segment in the parachain runtime
// is:
// UNINCLUDED_SEGMENT_CAPACITY = (2 + RELAY_PARENT_OFFSET) * BLOCK_PROCESSING_VELOCITY + 1.
//
// Since we only search for parent blocks which have already been imported,
// we can guarantee that all imported blocks respect the unincluded segment
// rules specified by the parachain's runtime and thus will never be too deep. This is just an extra
// sanity check.
const PARENT_SEARCH_DEPTH: usize = 40;
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@lexnv lexnv Feb 3, 2026

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Would it be worth bumping this to 256 instead? It might be a good safeguard, not sure what other defaults we have in code tho

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@bkchr bkchr Feb 3, 2026

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You can only go back to the included block and the list of pending blocks can not grow infinite.


// Helper to pre-connect to the backing group we got assigned to and keep the connection
// open until backing group changes or own slot ends.
struct BackingGroupConnectionHelper {
Expand Down Expand Up @@ -286,7 +273,6 @@ where
.await
.unwrap_or(DEFAULT_SCHEDULING_LOOKAHEAD)
.saturating_sub(1) as usize,
max_depth: PARENT_SEARCH_DEPTH,
ignore_alternative_branches: true,
};

Expand Down
40 changes: 11 additions & 29 deletions cumulus/client/consensus/common/src/parent_search.rs
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Expand Up @@ -42,9 +42,6 @@ pub struct ParentSearchParams {
/// A limitation on the age of relay parents for parachain blocks that are being
/// considered. This is relative to the `relay_parent` number.
pub ancestry_lookback: usize,
/// How "deep" parents can be relative to the included parachain block at the relay-parent.
/// The included block has depth 0.
pub max_depth: usize,
/// Whether to only ignore "alternative" branches, i.e. branches of the chain
/// which do not contain the block pending availability.
pub ignore_alternative_branches: bool,
Expand Down Expand Up @@ -78,18 +75,17 @@ impl<B: BlockT> std::fmt::Debug for PotentialParent<B> {
/// Perform a recursive search through blocks to find potential
/// parent blocks for a new block.
///
/// This accepts a relay-chain block to be used as an anchor and a maximum search depth,
/// along with some arguments for filtering parachain blocks and performs a recursive search
/// for parachain blocks. The search begins at the last included parachain block and returns
/// a set of [`PotentialParent`]s which could be potential parents of a new block with this
/// This accepts a relay-chain block to be used as an anchor along with some arguments for
/// filtering parachain blocks and performs a recursive search for parachain blocks.
/// The search begins at the last included parachain block and returns a set of
/// [`PotentialParent`]s which could be potential parents of a new block with this
/// relay-parent according to the search parameters.
///
/// A parachain block is a potential parent if it is either the last included parachain block, the
/// pending parachain block (when `max_depth` >= 1), or all of the following hold:
/// pending parachain block, or all of the following hold:
/// * its parent is a potential parent
/// * its relay-parent is within `ancestry_lookback` of the targeted relay-parent.
/// * its relay-parent is within the same session as the targeted relay-parent.
/// * the block number is within `max_depth` blocks of the included block
pub async fn find_potential_parents<B: BlockT>(
params: ParentSearchParams,
backend: &impl Backend<B>,
Expand All @@ -111,10 +107,6 @@ pub async fn find_potential_parents<B: BlockT>(
aligned_with_pending: true,
}];

if params.max_depth == 0 {
return Ok(only_included);
};

// Pending header and hash.
let maybe_pending = {
// Fetch the most recent pending header from the relay chain. We use
Expand Down Expand Up @@ -161,7 +153,7 @@ pub async fn find_potential_parents<B: BlockT>(

// If we want to ignore alternative branches there is no reason to start
// the parent search at the included block. We can add the included block and
// the path to the pending block to the potential parents directly (limited by max_depth).
// the path to the pending block to the potential parents directly.
let (frontier, potential_parents) = match (
&maybe_pending,
params.ignore_alternative_branches,
Expand All @@ -176,10 +168,8 @@ pub async fn find_potential_parents<B: BlockT>(
return Ok(Default::default());
}

// Add all items on the path included -> pending - 1 to the potential parents, but
// not more than `max_depth`.
let num_parents_on_path =
route_to_pending.enacted().len().saturating_sub(1).min(params.max_depth);
// Add all items on the path included -> pending - 1 to the potential parents.
let num_parents_on_path = route_to_pending.enacted().len().saturating_sub(1);
for (num, block) in
route_to_pending.enacted().iter().take(num_parents_on_path).enumerate()
{
Expand Down Expand Up @@ -208,10 +198,6 @@ pub async fn find_potential_parents<B: BlockT>(
_ => (only_included, Default::default()),
};

if potential_parents.len() > params.max_depth {
return Ok(potential_parents);
}

// Build up the ancestry record of the relay chain to compare against.
let rp_ancestry =
build_relay_parent_ancestry(params.ancestry_lookback, params.relay_parent, relay_client)
Expand All @@ -223,7 +209,6 @@ pub async fn find_potential_parents<B: BlockT>(
included_header,
maybe_pending.map(|(_, hash)| hash),
backend,
params.max_depth,
params.ignore_alternative_branches,
rp_ancestry,
potential_parents,
Expand Down Expand Up @@ -323,7 +308,6 @@ pub fn search_child_branches_for_parents<Block: BlockT>(
included_header: Block::Header,
pending_hash: Option<Block::Hash>,
backend: &impl Backend<Block>,
max_depth: usize,
ignore_alternative_branches: bool,
rp_ancestry: Vec<(RelayHash, RelayHash)>,
mut potential_parents: Vec<PotentialParent<Block>>,
Expand Down Expand Up @@ -355,7 +339,7 @@ pub fn search_child_branches_for_parents<Block: BlockT>(
let is_pending = pending_hash.as_ref().map_or(false, |h| &entry.hash == h);
let is_included = included_hash == entry.hash;

// note: even if the pending block or included block have a relay parent
// Note: even if the pending block or included block have a relay parent
// outside of the expected part of the relay chain, they are always allowed
// because they have already been posted on chain.
let is_potential = is_pending || is_included || {
Expand Down Expand Up @@ -385,13 +369,11 @@ pub fn search_child_branches_for_parents<Block: BlockT>(

if is_potential {
potential_parents.push(entry);
}

if !is_potential || child_depth > max_depth {
} else {
continue;
}

// push children onto search frontier.
// Push children onto search frontier.
for child in backend.blockchain().children(hash).ok().into_iter().flatten() {
tracing::trace!(target: PARENT_SEARCH_LOG_TARGET, ?child, child_depth, ?pending_distance, "Looking at child.");

Expand Down
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