Core backend concepts from concurrency and error handling to API design and service architecture.
Understand PostgreSQL internals from EXPLAIN plans to the storage engine, indexing strategies, and zero-downtime migration patterns.
Modern Java for backend services: virtual threads, GraalVM native images, streams pipelines, async composition, and an honest comparison against Go on a real workload.
Go context.Context: constructors, cancellation, deadlines, request values, and five goroutine leak patterns in production.
Kafka producer configuration: acks, idempotence, batching, compression, and the tradeoffs that matter for throughput and durability.
Postgres EXPLAIN plans: node types, cost interpretation, and six patterns that kill query performance on large datasets.
Handle unpredictable JSON in Go: map[string]any, json.RawMessage, type switches, and defensive patterns for shifting schemas.
Go graceful shutdown: SIGTERM handling, health probe coordination, and Kubernetes drain patterns for zero dropped requests.
Why exactly-once is a myth, and how idempotency keys, database constraints, and the outbox pattern make retries safe in Go and Java.
Java collections: computeIfAbsent, getOrDefault, removeIf, immutables, and Comparator chains that eliminate entire bug categories.
Stop fighting java.util.Date. Master LocalDateTime, ZonedDateTime, Instant, and Duration — predictable, thread-safe time handling.
Java singletons: enum patterns, double-checked locking, and holder-classes — and when dependency injection is the better answer.
Write tests that catch real bugs: JUnit 5 lifecycle, parameterized tests, Mockito, WireMock, Testcontainers, and mutation testing.