Backend case studies: the bottleneck, the design decision, and the verified result
SELECTED ENGINEERING CASES
A chat server designed to be shared by several games: channel-level Valkey sharding cut ACK p95 from 767.6ms to 6.6ms, and a dev load test held 20,002 CCU for 900s.
Single node → 4-shard cluster
3.3x the target concurrency sustained
Traced three RDS CPU/IO saturation cases to the offending query with Performance Insights and EXPLAIN: backfill throughput up 26x (9.3 → 247 items/min), and full scans of up to 36 minutes on a 26.37M-row audit log removed (EXPLAIN rows = 3).
26x · 15,333 completed, 0 pending
p99 67.0s → 2.99s
Realigned a game server's data-module fork that had drifted for 2+ years onto the shared npm package (610 files, 310+ imports migrated), automated upgrades across 7 projects with GitHub Actions (about 3 hours by hand → about 15 minutes), and cut the shared server kit's average test job time 61% (15m47s → 6m06s).
61% faster · whole CI about 16 → 7 min
7-project matrix in parallel
Owned design, operations, and merge approval for the company-wide device policy guard and usage collection server; AI coding agents handled implementation. The guard's policy path switched usage reporting on for 92 people, and all 87 reporting devices applied it. After two collection-server outages (2 days 18 hours, then 17 hours 40 minutes), memory limits were reordered as app < container < host and parsing moved to streaming, bringing the largest file's parse peak to 67% of a 640MiB limit.
92 people assigned · reporting online devices
Applied after a 2-day 18-hour 31-minute outage; a reparse loop remains the likely trigger