Маркіян

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

[відкрити контакти](див. вище в блоці «контактна інформація»)
PROFILE
[відкрити контакти](див. вище в блоці «контактна інформація») 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.