Nguyễn Tiến Đạt — Backend Engineer

API Billing Platform · abp

Concurrent merchant top-ups never lose an update, even under load.

load-tested

Atomic INSERT … ON CONFLICT DO UPDATE — not a read-then-write race — plus a DB-level unique constraint so double-subscribes can't slip through an app-level check.
Per-merchant Resilience4j bulkhead + circuit breaker, so one broken merchant can't starve every other tenant's requests.
Redis cache-aside for merchant routing/pricing (read:write ratio ~10⁵), with a fail-open CacheErrorHandler — a dead cache degrades the path, it doesn't take the gateway down.
RabbitMQ drives the operational write; the same event republishes to Kafka, partitioned by merchant, as a durable and independently replayable audit log.
Proven with dedicated k6 load tests and Testcontainers integration tests, not just unit coverage.

JavaSpring BootResilience4j KafkaRabbitMQRedisPostgreSQL

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Skolem

Two SQL queries are semantically equivalent — or here's the exact row where they disagree.

Z3-backed

Formal equivalence checking via Z3 SMT solving — deterministic proof, not linting or heuristics.
Three surfaces on one engine: a web UI, a CI/CD JSON endpoint, and an MCP server so AI coding agents call verification in-loop, powering a counterexample-driven self-healing repair.
Fails closed on unsupported SQL — an unencodable predicate is rejected, never silently dropped into a false "equivalent."
A divergent verdict is re-run against a concrete SQLite witness before being trusted, catching encoder bugs instead of showing a fake counterexample.
Auth, per-project API keys, Supabase/Postgres with RLS, billing via Lemon Squeezy, circuit breaker on LLM calls.

PythonFastAPIZ3 / SMTSupabaseDocker

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InstaClone

Sessions survive a horizontal scale-out, not just a single instance.

containerized

Google OAuth2 login via Spring Security with auto-provisioned users.
Redis-backed distributed HTTP sessions (Spring Session) — sessions live outside the JVM, so any instance can serve any request.
MinIO (S3-compatible) object storage for image uploads.
Centralized exception handling via @RestControllerAdvice, mapping domain exceptions to stable HTTP codes.
Full stack — MySQL, Redis, MinIO, backend — containerized with Docker Compose; API documented via auto-generated OpenAPI.

Java 21Spring Boot 3.5Spring SecurityRedisMySQLMinIO

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go-api-gateway

Routes can change at runtime — no restart, no hand-written SQL.

thread-safe

SQLite-backed route table matched on path, method, and header, behind a router guarded by sync.RWMutex — concurrent reads under exclusive writes.
Runtime admin API to register routes on the fly, persisted immediately for the next startup.
Two pluggable rate limiters (token bucket, fixed window) — defaults to token bucket to avoid the boundary-burst problem fixed windows allow at the edges.

GoSQLite

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arxiv-lens

Two extraction runs on the same papers must produce the same graph — or the build refuses to ship.

drift-gated

Closed ontology — 6 entity types, 6 relations with domain/range constraints — enforced as a decoding constraint on structured extraction, a mechanical repair rule for schema violations, and a canonicalization tiebreak, not schema-free extraction.
A structural drift gate diffs snapshot N against N+1 and exits non-zero the moment unchanged inputs produce a different graph, refusing to promote a bad build into Neo4j.
Z3 encodes the ontology's transitivity, asymmetry, and irreflexivity, surfacing a minimal unsat core for contradictions that span multiple papers — no single paper wrong on its own.
Two services glued by Kafka (async graph.updated) and gRPC (sync queries): a hexagonal Spring Boot query-service whose Caffeine cache-aside layer cuts /api/stats from a 4.1s cold traversal to 8ms cached.
Benchmarked against a conventional vector-RAG baseline on the same golden questions — full paper recall vs. 61% for vector search, and vector retrieval can't represent "no relationship exists" since top-k always returns k results.

JavaSpring BootPython KafkagRPCNeo4jZ3 / SMTDocker

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I prove backend systems are correct — not just that they compile.