Yan

Yan Serhiienko | Java Developer
Email: [відкрити контакти](див. вище в блоці «контактна інформація»)
Location: Kyiv, Ukraine
LinkedIn: [відкрити контакти](див. вище в блоці «контактна інформація»)
GitHub: https://github.com/seyan99
Telegram: https://t.me/seyan99

Professional Summary
Java Backend Developer 3 years of commercial experience, building and optimizing high-load backend systems using Java
and Spring Boot. Currently owning core backend functionality of a production CRM. 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, 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 (SaaS Advertisement / Marketing) - Java Developer
October 2023 - Present
Improved critical backend functionality performance by 10-15x through database optimization.
Reduced authentication subsystem load by ~30% by implementing Redis-based caching.
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