writeonce/docs/stories/databasev2/07-single-file-db.md
shoney.arickathil 566559cf70 docs: name the residency value keys, not index (review change)
- `resident: all | keys` replaces `resident: all | index`. Two reasons beyond
  taste: it kills the collision with the `index:` argument
  (`@table(index: [customer], resident: index)` read badly), and it puts both
  values on ONE axis — each now answers "what row data stays resident",
  where `all`/`index` mixed a quantity with a structure name
- accurate as well as clearer: what stays resident is the id->offset map, the
  secondary indexes and the unique shadows — all key structures; row payloads
  are exactly what leaves. `resident: none` was rejected as overclaiming,
  since the indexes very much are resident
- checked for collisions: neither `all` nor `keys` is a keyword or a builtin
  (`key_at`/`val_at` exist, bare `keys` does not)
- the spec's wart note became a recorded decision; the rejected spelling is
  kept quoted so the rationale still reads
- fixes a bug I introduced in the 2026-08-26 track move: all six moved
  iterations carried a banner reading "Part of [Story — the database beyond
  RAM]" whose link pointed at the LANGUAGE arc — correct target, lying text,
  the exact failure mode the link audit warned about. Banners now point at
  the databasev2 story, and the original "Part of" line says plainly which
  track the iteration was authored in before the move
- linkcheck 0 broken / 0 anchors

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-08-26 22:47:24 +02:00

3.6 KiB

track iteration was_language_iteration status
databasev2 7 33 refine

databasev2 7 — WO_DATA=<path>.db: the persistent store as one file

Moved 2026-08-26 from the language track, where this was iteration 33. Part of Story — databasev2: the database beyond RAM. Content unchanged by the move; its dependencies are restated in that track index.

Format: product/story-iteration-template. Part of Story — one language, one runtime, one database, one binary — the track this iteration was authored in before the 2026-08-26 move.

Inserted 2026-08-22 (developer ask: "can the persistent db be in file.db form?"). The truth is already almost there: WO_DATA=<dir> holds exactly ONE file (shard-0.wal) — the entire persistent state, since the log is the whole store and no data pages exist. This iteration makes the surface say so: point WO_DATA at a file and THAT file is the store. Small, driver-only, independent of the concurrency chain.

Goals

  • WO_DATA=<path> accepts a file path. A path that is not an existing directory is treated as THE wal file (app.db, store.wo.db — the name is the operator's). The directory form stays and keeps meaning <dir>/shard-0.wal — every existing deployment and gate is byte-identical.
  • One file remains the whole truth at any core count — stage 3 made the WAL owner-shard-only (shard 0 is the sole writer), so nothing multi-shard ever adds a second file.
  • The contract says it out loud: 04-db-binding.md documents the file form, and documents honestly that the file is an append-only log that grows until iteration 32 lands.

Acceptance Criteria

  • Given WO_DATA=/tmp/app.db (no such directory), when a program seeds, restarts, and verifies, then replay is byte-true and /tmp/app.db is the only artifact on disk.
  • Given WO_DATA=<dir> (existing directory), when the same program runs, then behavior is byte-identical to today — <dir>/shard-0.wal, every standing gate unchanged.
  • Given the db-bench durability legs pointed at the file form, when the restart proof and kill -9 battery run, then every guarantee holds identically (the file IS the same WAL, only named by the operator).

Out Of Scope

  • A paged database file (SQLite's shape) — still rejected; the disk story is the WAL, full stop.
  • Checkpoint/compaction — iteration 32's; its rename-swap (write snapshot+tail to a NEW file, fsync, rename() over the old) is exactly what keeps the single-file promise crash-safe when it lands. 33 before or after 32 works; landing 33 first means 32's spec inherits the file form as a stated constraint.
  • Multiple stores per process, attach-by-file — held iteration 20's territory.

Info

  • The whole change is runtime/src/main.c's hardcoded snprintf("%s/shard-0.wal", dir) growing a stat-based fork (directory → today's path; otherwise → the path itself), plus a gate check and the binding-doc note. No engine, no WAL format, no compiler.
  • Fork for the (tiny) spec: what does a NONEXISTENT path mean? Leaning: a path whose parent exists and that does not end in / is a file to create; a trailing / or existing directory keeps the directory form. Refusing ambiguity loudly (WO exit 2) beats guessing.

Proposed Solution

Small enough for a bounded slice: brainstorm the one fork in chat, implement driver + db-bench file-form leg + docs in one pass, gates green. No plan document needed unless it grows.