Spring Boot Testcontainers
Test against real databases and services in containers, manage their lifecycle, and isolate state between tests.
~2 min readread →
Developer interview notes & guides — Page 10
Focused explanations and longer guides, with worked scenarios, common mistakes and interview exercises across every chapter.
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Showing 217–240 of 825 articles
Spring Boot Distributed Tracing
Propagate trace context with Micrometer Tracing, correlate spans across services, and sample without overwhelming storage.
~2 min readread →
Spring Bean Validation Groups
Apply different validation rules for create and update with groups, and sequence checks with group order.
~2 min readread →
PostgreSQL CASE Expressions
Use simple and searched CASE for conditional values, ordering and aggregation, and avoid the NULL that a missing ELSE produces.
~2 min readread →
PostgreSQL Date Truncation and Ranges
Group by time with date_trunc, write range predicates with >= and < instead of BETWEEN, and handle timezones explicitly.
~2 min readread →
PostgreSQL Deadlocks and Retry
Prevent deadlocks with a consistent lock order and short transactions, and retry the ones you cannot prevent.
~2 min readread →
PostgreSQL Generated Columns
Keep derived values consistent with generated columns, choose STORED or virtual, and index a stored derived value.
~2 min readread →
SQL WHERE vs HAVING
Filter rows with WHERE before grouping and groups with HAVING after, and understand why the placement changes cost and correctness.
~2 min readread →
PostgreSQL JSONB Columns and Indexing
Store and query semi-structured data with jsonb, extract fields with -> and ->>, and index the queries you actually run.
~2 min readread →
PostgreSQL Recursive CTEs for Hierarchies
Walk parent-child data with WITH RECURSIVE, guard against infinite loops, and understand the anchor and recursive terms.
~2 min readread →
PostgreSQL Self-Joins
Join a table to itself to compare rows, walk a hierarchy, or find duplicates, and avoid the accidental cross product.
~2 min readread →
PostgreSQL Set Operations
Combine result sets with UNION, UNION ALL, INTERSECT and EXCEPT, and know when deduplication changes cost or meaning.
~2 min readread →
System Design: Backpressure and Load Shedding
Protect a service from overload by bounding queues, signaling producers to slow down, and shedding low-priority work.
~2 min readread →
System Design: Bloom Filters
Use a Bloom filter to skip lookups with a tiny memory footprint, and understand its false-positive-only guarantee.
~2 min readread →
System Design: Idempotent APIs
Make retried requests safe with idempotency keys, store the result per key, and return the original response on a repeat.
~2 min readread →
System Design: Leader Election and Fencing
Elect a single leader with leases or consensus, use fencing tokens to reject stale leaders, and avoid split brain.
~2 min readread →
System Design: Notification System
Ingest events, respect preferences, deduplicate and deliver across channels with retries and provider failover.
~2 min readread →
System Design: Presence Tracking
Track online status with heartbeats and TTLs, derive presence instead of storing it, and avoid fanning out to every client.
~2 min readread →
System Design: Schema Evolution
Evolve stored and message schemas with additive changes, expand-contract migrations, and reader tolerance across services.
~2 min readread →
System Design: Time-Series Metrics
Ingest metrics with bounded cardinality, roll up raw samples, and set retention tiers so storage stays predictable.
~2 min readread →
System Design: URL Shortener
Generate short codes from ids, keep the read path fast and cached, and handle collisions and analytics.
~2 min readread →
Testing Time with an Injected Clock
Inject a clock instead of calling the system time, freeze it in tests, and remove the sleeps that make tests flaky.
~2 min readread →
Code Coverage and Its Limits
Read line and branch coverage as a signal, not a goal, and avoid the tests that chase the number without checking behavior.
~2 min readread →
Scoping End-to-End Tests
Reserve end-to-end tests for critical user journeys, use stable selectors, and avoid duplicating coverage the lower tests already have.
~2 min readread →
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