Low-level design

Low-level design

OOP and SOLID class design for machine-coding LLD: interfaces, invariants, in-memory state, and concurrency you can implement and test.

• ArchiveSweep

  3 studies
  1. 1.ArchiveSweep (File Deduplication) LLD - Spec, Pipeline & ConceptsMachine-coding LLD: recursively scan a directory tree, skip symlinks, collapse hard links to one inode, then find byte-identical duplicate groups with a staged pipeline (size -> sample prefix -> streaming SHA-256 -> byte verify).
  2. 2.ArchiveSweep - Streaming SHA Solution & TestsFull runnable stdlib implementation: archive_sweep(root, workers) with scan, sample, stream hash, byte verify, ThreadPoolExecutor, and unittest coverage for duplicates, near-misses, symlinks, hard links, and empty files.
  3. 3.ArchiveSweep - Concurrency, Symlinks & Hardlink Edge CasesWhich stages parallelize safely, how to aggregate errors without losing groups, symlink policy, hardlink reclaim math, and how to explain the design without overselling hash equality.

• Comments and Replies

  3 studies
  1. 1.Comments and Replies LLD - Spec, Design Steps & ConceptsTwo-level in-memory comments/replies LLD: spec, structure choices, independent IDs, order, snapshots, concepts.
  2. 2.Comments and Replies - In-Memory Solution, Ordering & TestsFull CommentService Python+TS sketch with tests for order, validation, isolation, independent IDs, concurrency, snapshots.
  3. 3.Comments and Replies - Concurrent IDs, Snapshots & Post IsolationConcurrent ID allocation, defensive snapshots, post isolation, lock granularity decision chart, follow-ups.

• Feature Flag Service

  3 studies
  1. 1.Feature Flag Service LLD - Targeting, Sticky Buckets & Kill SwitchesProvisional machine-coding LLD for an in-memory flag service: kill switch, disabled, segment gate, then a sticky SHA-256 percentage.
  2. 2.Feature Flag Service - Sticky Bucket + Kill Switch Solution & TestsRunnable FlagStore with upsert, sticky SHA-256 bucketing, segment gates, kill-switch precedence, and a concurrent upsert/evaluate test.
  3. 3.Feature Flag Service - Evaluation Order & ConcurrencyWhy the kill switch short-circuits before the percentage, why get copies the flag, and how this round connects to progressive delivery.

• LLM Gateway Rate Limiter

  3 studies
  1. 1.Rate Limiter for an LLM Gateway - LLD Spec & ConceptsMachine-coding LLD for an in-process LLM gateway limiter: a per-tenant token bucket, an exact sliding-window log, and a composed decision with remaining and retry_after_ms.
  2. 2.Rate Limiter - Token Bucket + Sliding Window Solution & TestsRunnable TokenBucket, SlidingWindowLog, and GatewayLimiter, with a fake clock and an 80-thread burst flood.
  3. 3.Rate Limiter - Concurrency, Retry-After & CompositionWhy one RLock around the composed check still counts an RPM event when the burst denies, how retry_after_ms is computed, and how this round maps onto Redis Lua.