POC: aggregate post-block sync acknowledgements

[randomblocker]

Summary

This is a deliberately non-production POC for reducing the quadratic post-block synchronization burst in the current PoRBFT path.

The stabilisation branch currently lets every block signer publish the block, then lets each non-signing recipient broadcast its sync status to every peer. This branch puts that behavior behind a disabled-by-default flag and tests a smaller path:

• one deterministic committee publisher sends the confirmed block;
• recipients return their existing syncData in the block response;
• the publisher sends one bounded acknowledgement aggregate;
• periodic fast-sync and peer anti-entropy remain available for missed updates.

It does not change transaction validation, block construction, voting, or finality.

Empirical result

The same isolated six-node topology was measured in legacy and aggregate modes over five complete blocks, excluding startup traffic. The topology used a four-member shard and two non-signing recipients at a 20-second cadence.

Mode	Block deliveries	Sender status	Receiver status	Aggregate	Total calls/block
Legacy	8	24	12	0	44
Aggregate	2	0	0	5	7

That is an 84.1% reduction, exactly matching the source-derived model. All six nodes remained at the same height across both samples.

A recovery check stopped node 6 while the chain advanced, restarted it, and observed it automatically converge with node 1 at height 10 through the retained recovery path.

The guarded lightweight transport harness then ran five bursts each at 100, 250 and 500 virtual peers with simulated 20–300 ms latency, 5% transient failures and bounded retries:

Peers	Legacy calls/block	Aggregate calls/block	Reduction	Mean burst	Peak RSS
100	10,384	195	98.1%	504 ms	70 MB
250	63,484	495	99.2%	528 ms	104 MB
500	251,984	995	99.6%	810 ms	149 MB

Every delivery was admitted after bounded retries. The 500-peer aggregate was 34.4 KB and total sender traffic was 18.1 MB per block. A real multi-host test is still required; the emulator proves transport-path scaling but does not reproduce hundreds of databases, consensus engines, OmniProtocol connections or WAN kernels.

Safety and review gates

BLOCK_SYNC_AGGREGATION_ENABLED defaults to false. The POC must not be enabled on a public network yet.

Before production use, maintainers must decide and implement:

1. Per-recipient detached acknowledgement signatures, or a formally reviewed trust rule allowing a quorum block signer to relay liveness-only acknowledgements.
2. A mixed-version activation protocol so legacy and aggregate nodes cannot diverge during rollout.

Receivers fail closed unless the aggregate is bounded, matches a locally verified block, comes from a signer of that block, and names only known identities committed to the block peerlist/signatures. Applying an aggregate changes sync hints only; it never authenticates a peer or marks one online.

Included tooling

• feature-flagged protocol path and RPC handler;
• bounded aggregate validation/admission helpers;
• Prometheus counters separated by post-block source;
• six-node, loopback-only, resource-bounded Docker topology;
• reusable fixed-block measurement script;
• modeled and convergence tests through 500 peers;
• documented measurements and limitations.

Validation

• 15/15 focused aggregation tests passed (1,235 assertions).
• ESLint passed for all changed TypeScript implementation/test files.
• Bun production bundle completed successfully.
• Docker Compose configuration validated for the six-node topology.
• Six-node legacy and aggregate A/B completed with zero height spread.
• Offline-node recovery/convergence test passed.
• Secret scan and git diff --check passed.

Some existing consensus tests mix Jest APIs with bun:test imports and cannot all execute under one runner; that pre-existing runner incompatibility is not changed by this POC.

[coderabbitai]

Important

Review skipped

Draft detected.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: aaba5b05-ba62-4adf-900e-f36b0f435b2d

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}