docs: load-test evidence for the nano Postgres memory settings

[tonychang04]

What

Adds docs/pg-memory-loadtest-2026-07.md: A/B pgbench evidence (moderate load, heavy load, 90-connection storm, combined DB+vacuum+API stress) showing why the shipped docker-init/db/postgresql.conf memory settings exist.

Key result

On a 512MB nano host, stock Postgres defaults inside the ~150MB container limit get OOM-killed under a 90-connection storm (DB restart, 11 TPS, 6s avg latency, hung clients), while the shipped tuned conf fails fast and stays healthy (excess connections rejected, memory bounded, API on the same host still serving). Under heavy-but-legal load the tuned conf gives +8% TPS, half the swap traffic, and ~2x host headroom.

Also documents that the conf is bind-mounted from the host at provision time — hosts provisioned before the tuning landed need a re-copy + postgres restart to pick it up — and lists follow-up candidates (API image exec npm start double-wrapper, vm.swappiness on zram hosts, userland-proxy).

🤖 Generated with Claude Code

https://claude.ai/code/session_01J9NtiFkU34HQQgRSffNb4k

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Summary by cubic

Adds docs/pg-memory-loadtest-2026-07.md with load-test evidence for the tuned Postgres memory settings on nano hosts. Shows that the shipped docker-init/db/postgresql.conf avoids OOM under a 90-connection storm and delivers ~8% higher TPS with less swap on 512MB instances.

• Migration
  • If a host was provisioned before the tuning, re-copy the current postgresql.conf to the bind-mounted path and restart the Postgres container to apply it.

^{Written for commit 3ad4347. Summary will update on new commits.}

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