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Joonatan Saarhelo

PROFILE

Joonatan Saarhelo

Worked on core protocol and infrastructure for matter-labs/zksync-os and zksync-os-server, focusing on reliability, maintainability, and performance. Delivered features such as persistent RocksDB-backed Merkle trees, external node replay modes, and real-time L1 transaction streaming, while refactoring memory management and error handling for VM and bootloader components. Addressed serialization correctness, protocol versioning, and HTTP streaming compatibility to support robust node operations and seamless upgrades. Leveraged Rust, asynchronous programming, and low-level system design to improve memory safety, concurrency, and data integrity. The work emphasized backward compatibility, operational readiness, and scalable architecture across distributed blockchain execution environments and backend systems.

Overall Statistics

Feature vs Bugs

77%Features

Repository Contributions

19Total
Bugs
3
Commits
19
Features
10
Lines of code
9,622
Activity Months5

Work History

September 2025

4 Commits • 3 Features

Sep 1, 2025

September 2025 monthly summary: Across matter-labs/zksync-os and zksync-os-server, delivered reliability-focused features and critical fixes that strengthen EVM correctness, memory safety, versioned wire formats, and load-balancer-friendly streaming. Key work spanned two repositories with notable improvements in EVM bitwise operation handling, input handling refactor for bn254_ecadd_inner, versioned replay wire formats with immutability CI, and HTTP/1.0-compatible replay streaming.

August 2025

7 Commits • 2 Features

Aug 1, 2025

Concise monthly summary for 2025-08 focusing on business value and technical achievements for matter-labs/zksync-os-server. The month centered on delivering robust node capabilities, ensuring data integrity, and improving maintainability and ops readiness, with measurable impact on reliability, performance, and deployment readiness.

July 2025

4 Commits • 3 Features

Jul 1, 2025

Monthly summary for 2025-07 - matter-labs/zksync-os-server focused on delivering core resilience and real-time processing capabilities, along with consolidation of data access paths and configuration correctness.

June 2025

3 Commits • 1 Features

Jun 1, 2025

June 2025 – Matter Labs / zksync-os: Bootloader Core Refactor delivering unified error handling, streamlined calldata, and memory-safety improvements. The work consolidates deployment error paths, simplifies the bootloader loop, and enables the heap as scratch space through a slice-based calldata model and lifetime-safe data structures.

February 2025

1 Commits • 1 Features

Feb 1, 2025

February 2025 monthly summary for matter-labs/zksync-protocol focusing on memory model compatibility and protocol reliability. Delivered backward-compatible memory growth handling across VM versions and UMA opcode updates, refactored memory cost calculations, and aligned protocol behavior to support both legacy and modern VM flows. This work improves client compatibility, reduces memory-expansion risks, and paves the way for smoother upgrades.

Activity

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Quality Metrics

Correctness89.0%
Maintainability86.2%
Architecture87.0%
Performance83.6%
AI Usage21.0%

Skills & Technologies

Programming Languages

AssemblyBashDockerfileHTTPRustTokioTypeScript

Technical Skills

Asynchronous ProgrammingBackend DevelopmentBlockchainCI/CDCode RefactoringConcurrencyContainerizationCryptographyData StructuresDependency ManagementDevOpsDistributed SystemsEVMError HandlingEthereum

Repositories Contributed To

3 repos

Overview of all repositories you've contributed to across your timeline

matter-labs/zksync-os-server

Jul 2025 Sep 2025
3 Months active

Languages Used

RustDockerfileTokioTypeScriptBashHTTP

Technical Skills

Asynchronous ProgrammingBackend DevelopmentConcurrencyDependency ManagementEthereumMerkle Trees

matter-labs/zksync-os

Jun 2025 Sep 2025
2 Months active

Languages Used

RustAssembly

Technical Skills

BlockchainExecution EnvironmentsLifetimesLow-Level DevelopmentLow-Level ProgrammingMemory Management

matter-labs/zksync-protocol

Feb 2025 Feb 2025
1 Month active

Languages Used

Rust

Technical Skills

Low-Level ProgrammingMemory ManagementRustVM Development