Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Make approval-distribution aggression a bit more robust and less spammy #6696

Draft
wants to merge 1 commit into
base: alexggh/fix_possible_bug
Choose a base branch
from
Draft

Make approval-distribution aggression a bit more robust and less spammy #6696

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
116 changes: 96 additions & 20 deletions polkadot/node/network/approval-distribution/src/lib.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -318,7 +318,7 @@ impl Default for AggressionConfig {
fn default() -> Self {
AggressionConfig {
l1_threshold: Some(16),
l2_threshold: Some(28),
l2_threshold: Some(64),
resend_unfinalized_period: Some(8),
}
}
Expand Down Expand Up @@ -514,6 +514,8 @@ struct BlockEntry {
vrf_story: RelayVRFStory,
/// The block slot.
slot: Slot,
/// Backing of from re-sending messages to peers.
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
/// Backing of from re-sending messages to peers.
/// Backing off from re-sending messages to peers.

last_resent_at_block_number: Option<u32>,
}

impl BlockEntry {
Expand Down Expand Up @@ -880,6 +882,7 @@ impl State {
candidates_metadata: meta.candidates,
vrf_story: meta.vrf_story,
slot: meta.slot,
last_resent_at_block_number: None,
});

self.topologies.inc_session_refs(meta.session);
Expand Down Expand Up @@ -1319,6 +1322,33 @@ impl State {
self.enable_aggression(network_sender, Resend::No, metrics).await;
}

// When finality is lagging as a last resort nodes start sending the messages they have
// multiples times. This means it is safe to accept duplicate messages without punishing the
// peer and reduce the reputation and can end up banning the Peer, which in turn will create
// more no-shows.
fn accept_duplicates_from_validators(
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

It would safer to accept only a bounded amount of duplicates over time.

blocks_by_number: &BTreeMap<BlockNumber, Vec<Hash>>,
topologies: &SessionGridTopologies,
aggression_config: &AggressionConfig,
entry: &BlockEntry,
peer: PeerId,
) -> bool {
let topology = topologies.get_topology(entry.session);
let min_age = blocks_by_number.iter().next().map(|(num, _)| num);
let max_age = blocks_by_number.iter().rev().next().map(|(num, _)| num);

// Return if we don't have at least 1 block.
let (min_age, max_age) = match (min_age, max_age) {
(Some(min), Some(max)) => (*min, *max),
_ => return false,
};

let age = max_age.saturating_sub(min_age);

aggression_config.should_trigger_aggression(age) &&
topology.map(|topology| topology.is_validator(&peer)).unwrap_or(false)
}

async fn import_and_circulate_assignment<A, N, RA, R>(
&mut self,
approval_voting_sender: &mut A,
Expand Down Expand Up @@ -1390,13 +1420,22 @@ impl State {
"Duplicate assignment",
);

modify_reputation(
&mut self.reputation,
network_sender,
if !Self::accept_duplicates_from_validators(
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

above log could show if duplicate is accepted.

&self.blocks_by_number,
&self.topologies,
&self.aggression_config,
entry,
peer_id,
COST_DUPLICATE_MESSAGE,
)
.await;
) {
modify_reputation(
&mut self.reputation,
network_sender,
peer_id,
COST_DUPLICATE_MESSAGE,
)
.await;
}

metrics.on_assignment_duplicate();
} else {
gum::trace!(
Expand Down Expand Up @@ -1712,6 +1751,9 @@ impl State {
assignments_knowledge_key: &Vec<(MessageSubject, MessageKind)>,
approval_knowledge_key: &(MessageSubject, MessageKind),
entry: &mut BlockEntry,
blocks_by_number: &BTreeMap<BlockNumber, Vec<Hash>>,
topologies: &SessionGridTopologies,
aggression_config: &AggressionConfig,
reputation: &mut ReputationAggregator,
peer_id: PeerId,
metrics: &Metrics,
Expand Down Expand Up @@ -1746,14 +1788,21 @@ impl State {
?approval_knowledge_key,
"Duplicate approval",
);

modify_reputation(
reputation,
network_sender,
if !Self::accept_duplicates_from_validators(
blocks_by_number,
topologies,
aggression_config,
entry,
peer_id,
COST_DUPLICATE_MESSAGE,
)
.await;
) {
modify_reputation(
reputation,
network_sender,
peer_id,
COST_DUPLICATE_MESSAGE,
)
.await;
}
metrics.on_approval_duplicate();
}
return false
Expand Down Expand Up @@ -1845,6 +1894,9 @@ impl State {
&assignments_knowledge_keys,
&approval_knwowledge_key,
entry,
&self.blocks_by_number,
&self.topologies,
&self.aggression_config,
&mut self.reputation,
peer_id,
metrics,
Expand Down Expand Up @@ -2255,18 +2307,42 @@ impl State {
&self.topologies,
|block_entry| {
let block_age = max_age - block_entry.number;
// We want to resend only for blocks between min_age and min_age +
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I believe it should be sufficient that we trigger aggression only for oldest unfinalized block. From what I've seen in production and testing is that usuallt are a few unapproved candidates holding finality on a particular block.

Resending for all unfinalized blocks doesn't really make sense, it's better to make small incremental progress than send large bursts of messages. So I would just remove the resend_unfinalized_period parameter and code.

Am I missing anything ?

Copy link
Contributor Author

@alexggh alexggh Nov 29, 2024 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Am I missing anything ?

I don't think you are, I was think about the same thing, but I did not know the initial reason for using resend_unfinalized_period so I was trying to avoid it entirely, so yeah I'll look into resending it just for the last unfinalized.

// resend_unfinalized_period, there is no point in resending for blocks newer than
// that, because we are just going to create load and not gain anything.
let diff_from_min_age = block_entry.number - min_age;

// We want to back-off on resending for blocks that have been resent recently, to
// give time for nodes to process all the extra messages, if we still have not
// finalized we are going to resend again after unfinalized_period * 3 since the
// last resend.
let blocks_since_last_sent = block_entry
.last_resent_at_block_number
.map(|last_resent_at_block_number| max_age - last_resent_at_block_number);

let can_resend_at_this_age = blocks_since_last_sent
.zip(config.resend_unfinalized_period)
.map(|(blocks_since_last_sent, unfinalized_period)| {
blocks_since_last_sent > unfinalized_period * 3
})
.unwrap_or(true);

if resend == Resend::Yes &&
config
.resend_unfinalized_period
.as_ref()
.map_or(false, |p| block_age > 0 && block_age % p == 0)
{
config.resend_unfinalized_period.as_ref().map_or(false, |p| {
block_age > 0 &&
block_age % p == 0 && diff_from_min_age < *p &&
can_resend_at_this_age
}) {
// Retry sending to all peers.
for (_, knowledge) in block_entry.known_by.iter_mut() {
knowledge.sent = Knowledge::default();
}

block_entry.last_resent_at_block_number = Some(max_age);
gum::debug!(
target: LOG_TARGET,
block_number = ?block_entry.number,
"Aggression enabled with resend for block",
);
true
} else {
false
Expand Down
Loading