https://articles.hamzawi.dev/ One engineering concept a day. en https://articles.hamzawi.dev/lww-clock-skew https://articles.hamzawi.dev/lww-clock-skew Sat, 17 Oct 2026 00:00:00 GMT system design Your "Latest" Timestamp Is Lying. updated_at doesn't measure when something happened. It measures what some machine's clock said when the code ran. Those are different numbers, and on a fleet of nodes they… https://articles.hamzawi.dev/semantic-caching-llm https://articles.hamzawi.dev/semantic-caching-llm Fri, 16 Oct 2026 00:00:00 GMT ai engineering Build It In 12 Lines, Then See Where It Bites. Your support bot answers "how do I reset my password?" 400 times a day. Each one is a fresh generation: ~1.4s, ~$0.004. An exact-match cache catches almost none of them,… https://articles.hamzawi.dev/idle-timeout-mismatch https://articles.hamzawi.dev/idle-timeout-mismatch Wed, 14 Oct 2026 00:00:00 GMT cloud infrastructure The Silent Hang-Up. Keep-alive is a phone line left open between calls. Your load balancer keeps a pool of open lines to each backend so it doesn't pay a TCP+TLS handshake per request. https://articles.hamzawi.dev/property-based-testing https://articles.hamzawi.dev/property-based-testing Tue, 13 Oct 2026 00:00:00 GMT developer tooling 97% Coverage, One Missing Example. A booking service merges a user's busy intervals (minutes since midnight) before computing free slots: https://articles.hamzawi.dev/srcset-vs-picture https://articles.hamzawi.dev/srcset-vs-picture Mon, 12 Oct 2026 00:00:00 GMT web development Who Actually Picks The Image. img + srcset/sizes = you let the BROWSER choose. https://articles.hamzawi.dev/uuid-v4-vs-v7-primary-keys https://articles.hamzawi.dev/uuid-v4-vs-v7-primary-keys Sun, 11 Oct 2026 00:00:00 GMT databases The Cost Isn't The 16 Bytes. The width is a rounding error. What hurts is insert order. 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A PDB is a permission desk standing between your pods and anything that wants to politely remove one. https://articles.hamzawi.dev/shallow-vs-partial-clone https://articles.hamzawi.dev/shallow-vs-partial-clone Wed, 07 Oct 2026 00:00:00 GMT developer tooling Two Ways to Not Download Your Repo. Monorepo: 2.1 GB, 180k commits. CI spends 95s cloning before a single test runs. You reach for --depth=1, your "git diff against main" breaks, you set fetch-depth: 0, and… https://articles.hamzawi.dev/inp-long-tasks-yielding https://articles.hamzawi.dev/inp-long-tasks-yielding Tue, 06 Oct 2026 00:00:00 GMT web development Your Handler Was Fast, the Main Thread Wasn't. Your search box filters a 5,000-row table. You profile the keypress handler: 0.9ms. Lighthouse gives you 98. You ship. https://articles.hamzawi.dev/lock-queue-alter-table https://articles.hamzawi.dev/lock-queue-alter-table Mon, 05 Oct 2026 00:00:00 GMT databases Why a "Safe" Migration Froze Your Whole Table. 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Your payment service — 40 pods, private subnet, one NAT gateway — starts throwing: https://articles.hamzawi.dev/build-cache-timestamps-vs-hashes https://articles.hamzawi.dev/build-cache-timestamps-vs-hashes Thu, 01 Oct 2026 00:00:00 GMT developer tooling Timestamps vs Content Hashes. "My build is incremental, so it only rebuilds what actually changed." https://articles.hamzawi.dev/font-loading-display-metric-overrides https://articles.hamzawi.dev/font-loading-display-metric-overrides Wed, 30 Sep 2026 00:00:00 GMT web development font-display & Metric Overrides. A web font is not a stylesheet. It's a late-arriving image that your text is shaped by. Until it lands the browser must choose: show nothing, or show something wrong. That… https://articles.hamzawi.dev/index-only-scans-visibility-map https://articles.hamzawi.dev/index-only-scans-visibility-map Tue, 29 Sep 2026 00:00:00 GMT databases Debug-Along. Dashboard query, 400ms p95. There IS an index. EXPLAIN says it's used. 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Since 2017 AWS spot prices are smoothed — they drift slowly with long-term supply and demand, and everyone in a pool pays the same current price. Bidding high buys you almost… https://articles.hamzawi.dev/stdio-buffering-line-vs-block https://articles.hamzawi.dev/stdio-buffering-line-vs-block Fri, 25 Sep 2026 00:00:00 GMT developer tooling Why Your Logs Disappear The Moment You Pipe Them. Your worker prints progress every second. Run it in the terminal: perfect, one line per second. https://articles.hamzawi.dev/bfcache-back-forward-cache https://articles.hamzawi.dev/bfcache-back-forward-cache Thu, 24 Sep 2026 00:00:00 GMT web development Your Page Isn't Reloading, It's Waking Up. When a user hits Back, the browser doesn't have to re-run your page. Modern browsers snapshot the whole thing — DOM, JS heap, scroll position, closures, your Redux store — and… https://articles.hamzawi.dev/prepared-statements-generic-plan https://articles.hamzawi.dev/prepared-statements-generic-plan Wed, 23 Sep 2026 00:00:00 GMT databases Custom Plan vs Generic Plan. Your query ran in 3ms. Same query, same params, 10 minutes later: 400ms. Nothing deployed. No data grew. Welcome to the 6th execution. https://articles.hamzawi.dev/agent-loop-tool-use-contract https://articles.hamzawi.dev/agent-loop-tool-use-contract Tue, 22 Sep 2026 00:00:00 GMT ai engineering Tool Use Is a Contract, Not a Function Call. msgs = [{"role": "user", "content": "Why is checkout 500ing?"}] https://articles.hamzawi.dev/cross-az-traffic-zone-aware-routing https://articles.hamzawi.dev/cross-az-traffic-zone-aware-routing Mon, 21 Sep 2026 00:00:00 GMT cloud infrastructure The Bill Line Nobody Can Explain. Your cluster is healthy. p99 is fine. Then finance forwards the invoice: https://articles.hamzawi.dev/leases-fencing-tokens https://articles.hamzawi.dev/leases-fencing-tokens Sun, 20 Sep 2026 00:00:00 GMT system design Why Your Distributed Lock Isn't Safe. A distributed lock does NOT guarantee mutual exclusion over the resource. It only guarantees that two workers don't both hold the lock. Those are different things, and the gap… https://articles.hamzawi.dev/merge-queues-semantic-conflicts https://articles.hamzawi.dev/merge-queues-semantic-conflicts Sat, 19 Sep 2026 00:00:00 GMT developer tooling PR #412 renames a helper: getUser(id) → fetchUser(id). CI green ✅ https://articles.hamzawi.dev/service-worker-update-lifecycle https://articles.hamzawi.dev/service-worker-update-lifecycle Fri, 18 Sep 2026 00:00:00 GMT web development Build One in 14 Lines, Then Meet the Trap. Fast, offline-capable — and it will serve a broken '/' forever if you ship a bug, because a cached HTML hit never consults the network. https://articles.hamzawi.dev/explain-analyze-estimated-vs-actual-rows https://articles.hamzawi.dev/explain-analyze-estimated-vs-actual-rows Thu, 17 Sep 2026 00:00:00 GMT databases Estimated vs Actual Rows. Postgres does not know your data. Before running a query it places a BET: "this WHERE clause will match about 50 rows." From that guess it picks the strategy — index scan or…