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Yan Serhiienko | Java Developer
Email: [open contact info](look above in the "contact info" section)
Location: Kyiv, Ukraine
LinkedIn: [open contact info](look above in the "contact info" section)
GitHub: https://github.com/seyan99
Telegram: https://t.me/seyan99

Professional Summary
Java Backend Developer with 3+ years of software development experience (including 2 years of production/commercial
experience) building and optimizing high-load backend systems using Java and Spring Boot. Currently owning core
backend functionality of a production CRM processing ~500k requests/day. Strong background in backend performance
optimization, PostgreSQL tuning, production troubleshooting, CI/CD, monitoring and mentoring junior developers.

Technical Skills
 Languages: Java 11, Java 17, SQL
 Backend: Spring Boot, Spring MVC, Spring Data JPA, Hibernate, REST APIs, Multithreading / Concurrency, OOP, Design
Patterns, Transactions
 Databases & Caching: PostgreSQL, Redis, SQL Query Tuning, Index Optimization
 Messaging: Apache Kafka
 Testing: JUnit, Mockito, Playwright, Postman, Jmeter
 DevOps & Infrastructure: Docker, Jenkins CI/CD, Kubernetes, Linux
 Monitoring: Prometheus, Grafana
 Build & Version Control: Maven, Git
 Methodologies: Agile, CI/CD, Code Review, Mentoring

Professional Experience
Quantum Projects - Java Developer
October 2024 - Present
 Improved critical backend functionality performance by 10-15x through database optimization.
 Reduced authentication subsystem load by ~30% by implementing Redis-based caching (900k+ requests/day).
 Optimized PostgreSQL queries and indexes for a ~20GB production database.
 Designed and implemented IP whitelist management system.
 Developed Slack notification system later adopted as a business feature.
 Built statistics and monitoring tools for external API integrations.
 Implemented Prometheus and Grafana monitoring.
 Improved Jenkins CI/CD pipelines; Automated database migration between Kubernetes test environments.
 Improved E2E testing reliability.
 Led backend refactoring initiatives.
 Mentored 2 Junior Developers; Conducted 9 technical interviews.

Education
 GoIT - Java Developer Program (2022 - 2023)
 National Aviation University - Industrial and Civil Engineering (2014 - 2020)

Languages
 English - B2
 Ukrainian - C2