| Report Date | Date of submission (2025/04/16) |
| Submitted by | Alin Dima |
@alin:parity.io148f8D1P4CP2tV8JuaVHzEXQQgj3jBxEg3k9qZydPzkJjbQGSince joining the Polkadot Fellowship on April 26, 2024, I’ve spent the past year—and nearly two years overall as a full-time contributor—working deeply across critical areas of the Polkadot stack. My focus spans parachain consensus, elastic scaling, availability, and the collator protocol. The contributions I’ve made during this time reflect a high level of technical competency, autonomy, leadership and commitment, which I believe justifies my promotion from Rank I to Rank II.
My most notable contributions are centered around the following large protocol-level enhancements:
Data availability recovery has long been a bottleneck for Polkadot validator nodes, due in large part to the computational cost of Reed-Solomon erasure coding. Recognizing this as a core obstacle to scaling the number of parachain cores on Polkadot and Kusama, I led the initiative to optimize this subsystem both at the protocol and implementation level.
The most significant improvement came through implementing systematic recovery, a protocol upgrade that eliminates the decoding overhead in most cases by leveraging the property that the first third of the encoded chunks are unaltered copies of the original data. In tandem with this, I also optimized the underlying Reed-Solomon implementation itself, resulting in a combined reduction of approximately 60% in CPU usage for large PoVs, validated by benchmarks on private testnets.
To enable these changes, I undertook several foundational updates. First, I refactored the availability-recovery subsystem to follow a strategy pattern, improving extensibility and allowing graceful failovers. I authored RFC47, which introduced a canonical shuffling of chunk indices to balance bandwidth usage and provided a roadmap for protocol upgrade and deployment. The Fellowship accepted this RFC.
Ensuring compatibility between protocol versions, I added fallback support to Substrate networking and implemented a NodeFeatures runtime primitive to coordinate feature enablement across validators. This primitive has since been adopted by other key subsystems, such as elastic scaling.
The systematic recovery strategy and new protocol were delivered via the main subsystem implementation, with extensive integration tests. Additionally, I optimized the Cumulus recovery procedure to avoid unnecessary re-encoding, further reducing CPU consumption.
In parallel, I investigated the performance disparity between our Rust implementation of Reed-Solomon and Kagome’s C++ version. After deep profiling—including analysis at the assembly level—I identified key inefficiencies and proposed solutions (analysis here). This led to a series of micro-optimizations, performance fixes, and code improvements that significantly improved the performance of the Rust implementation.
All of this work has been successfully audited, with no security findings logged.
Elastic scaling is one of Polkadot’s most ambitious recent upgrades, allowing parachains to scale up by occupying more than one core. I was one of the core engineers driving this effort, collaborating closely with @sandreim and @skunert. My role involved deep work across the runtime, and different node subsystems. This was a complex protocol-level project which is crucial for the scaling strategy of parachains like Mythos and Asset hub.
On the relay chain, I implemented the runtime changes necessary to support multiple backed candidates per parachain. This lifted a core limitation and enabled parallel backing. I extended these capabilities to the provisioner subsystem via PR 3233 and PR 3778, enabling nodes to handle multiple candidates per para.
To support out-of-order backing, I rewrote the prospective-parachains subsystem, which was a critical bottleneck. This was a very complex endeavour that I owned. The resulting updates are captured in PR 4035 and PR 4937.
Elastic scaling also required updates to Cumulus, including support in the PoV recovery component, which I delivered in PR 4733. To support adoption, I authored a comprehensive documentation guide for parachain teams.
Getting the elastic scaling feature from the MVP to the production status involved two threads of work: RFC103 and deprecating AsyncBackingParams.
RFC103 addresses a potential vulnerability where a collator could distribute the same collation to all backing groups. I contributed numerous times to the node-side implementation (https://github.com/paritytech/polkadot-sdk/pull/6011, https://github.com/paritytech/polkadot-sdk/pull/5908) and owned the Cumulus-side support: https://github.com/paritytech/polkadot-sdk/pull/5372, https://github.com/paritytech/polkadot-sdk/pull/5888.
To enable dynamic resource allocation, I removed support for scheduling
TTL from the coretime assignment pallet and
deprecated AsyncBackingParams, which had
become obsolete with the introduction of the claim queue concept. Removing these static parameters
reduced validator overhead and improved spam resistance.
In parallel, I participated in the design of streamlined block production, proposing a simplified post-state-based approach. I developed a proof of concept and tested it using gluttons and spammening parachains. While the need for this implementation hasn’t yet materialized, the groundwork remains valuable for future scaling needs and showcases my ability to innovate and meaningfully contribute to areas outside of my previous expertise.
The remaining work needed for the elastic scaling production launch is tracked here.
In an effort to enhance the reliability of the parachain backing process, I started leading a comprehensive revamp of the collator protocol, introducing a persistent reputation system for collators. This project builds on previous issues raised in the ecosystem (reference) and collaborative discussions with other fellows.
I created a detailed proposal, currently under private review (which will soon make it to an RFC), and outlined the development process (which I'm managing) in an open project plan.
Early implementation work has already been merged or is in review. This includes a new UMP
signal that allows parachains to attribute
block-building merit to specific PeerIds—a key mechanism for enabling collator accountability.
Additionally, I authored the reputation-based peer
manager, which will manage peer connections
based on historical behavior.
Beyond these major initiatives, I’ve continued to contribute across the codebase with bug fixes, refactors, and performance enhancements. I actively review work in the areas of availability, consensus, and collator protocol, and regularly provide technical support to other contributors.
Provide your voting record in relation to required thresholds for your rank.
| Ranks | Activity thresholds | Agreement thresholds | Member's voting activities | Comments |
|---|---|---|---|---|
| I | 90% | N/A | I have voted on 0 out of 0 referenda in which I was eligible to vote (i.e 100 % voting activity) | There were no referendums available for my rank to vote on. |
| II | 80% | N/A | ||
| III | 70% | 100% | ||
| IV | 60% | 90% | ||
| V | 50% | 80% | ||
| VI | 40% | 70% |
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