Маркіян

MARKIIAN POTIUK
B A C K E N D D E V E L O P E R

[open contact info](look above in the "contact info" section)
PROFILE
[open contact info](look above in the "contact info" section) Backend Developer with 1.5 years of commercial experience on the
Corezoid ecosystem for passenger services (Telegram, Viber).
Lviv, Ukraine Focused on payment and booking flows: transaction safety,
PostgreSQL query performance and well-tested REST APIs.
Telegram Main stack: Node.js, Python, TypeScript, PostgreSQL, Redis, Corezoid,
Docker, pytest, Jira, Git
LinkendIn
EXPERIENCE
GitHub BACKEND DEVELOPER
Product company in passenger services (NDA), via outsourcing
SKILLS agency
2025 Apr - Present
Backend: Node.js, Python, Java,
Helped speed up schedule-search and booking-status endpoints
Golang, Redis
(p95 ~750 ms → ~140 ms): analyzed slow queries with EXPLAIN ANALYZE
Frontend: JavaScript, and, after review with the team lead, added a composite index
TypeScript, Angular (from_station, to_station, travel_date). [Helped verify the result with a
Databases: PostgreSQL, MySQL Python load-test script written by the team.]

Build & Deploy: Docker, Maven, Implemented Redis caching for schedule endpoints per the team's
design: -60% DB load at peak, 75% hit rate. Used a 7-min TTL (up to 7
Git
min of stale data is acceptable); seat availability stays uncached so a
Architecture: RESTful APIs &
seat can't be sold twice.
Transactions
Developed ticket-refund REST endpoints with another backend
Infrastructure: Linux, Networking
developer, following the analyst's spec: deadlines and fees are
English - B2 validated on the server with clear error codes; invalid client requests
-35%.

EDUCATION Wrote unit and integration tests for payment logic as part of the
team's coverage push (to 75%): duplicate transactions via
ASSOCIATE DEGREE IN
idempotency keys, gateway timeouts. Regression bugs per release
COMPUTER SCIENCE
dropped from 6 to 2. Extended the team's Python mock of the
Technological College of Lviv
Polytechnic National University payment provider for fast, stable tests.

2022 - 2026 Fixed bugs in booking and payment flows: reproduced them from logs
and Jira tickets, found the root cause, shipped the fix with a regression
test, and described the cause in the PR for the team.
Maintained Corezoid processes with the team: helped add structured
error logging with correlation IDs (payment-provider failure detection
~2 h → 15-20 min) and took part in splitting a legacy reservation
process into 7 named states.[Wrote small Python scripts to parse logs
and check data for support requests. Regular participant in code
reviews.