shoney.arickathil
c3741262cb
- database/src/wal.{c,h}: framed records len|crc32|payload|mark
("WOL1" written last -- no mark, no record), typed-row payloads
walking the class-table kinds (nested records, containers, nil
encodings), little-endian like the loader
- commit order verbatim from the shipped phase-D pattern: RAM apply,
stage, ONE pwrite + ONE fdatasync for the batch, ack after -- group
commit is everything staged riding one sync
- replay decodes straight into engine-owned values (no VM at boot)
and re-enters rows through the choke-point row API, so Task 4's
indexes will rebuild for free; next_id advances past replayed ids
this shard owns (wo_row_create_raw)
- torn tail = short/CRC-fail/no-mark/zero-len: intact prefix applies,
tear dropped whole, wo_wal_open positions AT the tear so the next
commit overwrites it; CRC-valid-but-undecodable = corruption, loud
- wo_wal_check: offline oracle, no engine needed -- the crash
battery's verifier
- test_wal 90/0 ASan+UBSan incl. five crash-battery rounds (fork,
insert/commit/ack-over-pipe, SIGKILL mid-stream: zero acked-but-
missing, zero acked-but-wrong); all runtime suites green, oop-e2e
71/0; binding doc WAL section + CODE-LOGIC + plan Task 2 checked
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
115 lines
5.6 KiB
Markdown
115 lines
5.6 KiB
Markdown
# DB binding — row format, id discipline, WAL layout, query subset
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> Normative companion to the engine plan
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> ([`2026-08-01-db-engine-binding.md`](../../superpowers/plans/2026-08-01-db-engine-binding.md)),
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> the way `00-wob-format.md` is normative for the image. Grows with the
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> plan's tasks; this revision covers **Task 1 (row storage)**. Memory-safety
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> doctrine lives in the 9b design's section 6 (the copy bulkhead) — this doc
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> is the *format*.
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## Two memory worlds, one crossing rule
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Rows store **no VM pointer**, ever. Values cross from VM heap to row storage
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by copy on insert, and back by copy on read (`wo_row_read` allocates fresh VM
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values from the shard's runtime). The engine's own allocations are plain
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malloc — never the VM arena, so table growth cannot eat the program's heap
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cap, and a heap-exhausted program can still read its data.
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## Row format
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```
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row := header slots
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header := id u64 | class_id u32 | flags u32 (16 bytes)
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slots := field_cnt × u64, declaration order (the VM object shape)
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```
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One 8-byte slot per field, kind-driven — the same kind bytes the `.wob`
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class table carries, walked the same way the VM walks them:
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| kind | slot holds | engine-owned shape |
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| --- | --- | --- |
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| `SCALAR` | the 8 bytes themselves | — (`WO_NIL_SCALAR` spells a `?scalar` nil) |
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| `TEXT` | pointer, 0 = nil | `db_text { len u32; bytes[] }` |
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| `OWNED` | pointer, 0 = nil | `db_rec { class_id u32; slots[] }` — flattened by value, recursively through these same rules |
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| `MULTI` | pointer, 0 = nil | `db_multi { elem_kind u8; len u32; items[] }`, elements encoded element-wise |
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| `MAP` | pointer, 0 = nil | `db_map { key_kind, val_kind u8; len u32; kv pairs }` |
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| `GCREF` | **never stored** | compile error upstream (the GC bulkhead); the engine refuses it defensively as an encode error |
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`ref T` is a `SCALAR` at this layer — the target row's id. The engine learns
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what it references only when the FK checks land (9b plan, Task 3).
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## Storage
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Per shard, per class, created lazily on first insert:
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- **Slabs** of 256 rows (`DB_SLAB_ROWS`), malloc'd, **never moved or freed
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while the table lives** — a row's address is stable for its lifetime,
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which is the property 9b's loop-scoped row views stand on.
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- An **occupancy bitmap** (one bit per slot, slab-major) and a LIFO
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**free-slot list**: removal recycles the slot; a recycled slot is always
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used before a new slab grows. Ids are never reused; slots are.
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- The **primary index**: an open-addressing hash, id → slot, splitmix64
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finalizer, power-of-two capacity, 0.7 load, tombstoned deletes (ids are
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never 0 and never reused, so the all-ones sentinel cannot collide).
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## Id discipline
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Per table, per shard: shard S of N allocates `S+1, S+1+N, S+1+2N, …` — the
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c-runtime plan's shipped interleave. Creation is coordination-free; a row's
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owner shard is `(id-1) % N`. Milestone 1 runs at N=1 and everything
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degenerates to `1, 2, 3, …`. Id 0 does not exist (it is the hash's "empty"
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and the `?ref`'s nil).
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## Choke points
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`wo_row_insert` and `wo_row_remove` are the only functions that mutate a
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table. Task 4's secondary indexes hook exactly these two sites (marked
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`INDEX HOOK` in `database/src/table.c`); the WAL (Task 2) stages its record
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beside the same calls. Anything else touching a slab is a defect by
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definition — the doctrine the Rust engine learned and this engine enforces.
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## WAL (Task 2) — `database/src/wal.{c,h}`
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Record framing, replay-whole-or-not-at-all:
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```
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record := len u32 | crc u32 | payload | mark u32
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len = payload bytes (never 0: a zero length is the preallocated tail)
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crc = CRC32 (poly 0xEDB88320) of the payload
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mark = 0x574F4C31 "WOL1", the last bytes of the record — a record
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without its mark is torn by definition
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payload := kind u8 | class_id u32 | row_id u64 | body
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kind = 1 insert (body = fields), 2 remove (no body), 3 update (Task 5)
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```
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Body fields walk the class table's kinds: `SCALAR` 8 bytes; `TEXT` u32 len +
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bytes (`0xFFFFFFFF` = nil); `OWNED` presence u8 then class id + fields
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recursively; `MULTI` presence + elem kind + len + elements; `MAP` presence +
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both kinds + len + pairs. Little-endian, same platform note as the loader.
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**Commit order (doctrine, verbatim from the shipped phase-D pattern):** RAM
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apply → stage record → `wo_wal_commit` (one pwrite of the batch + one
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fdatasync) → only then acknowledge. Group commit = everything staged since
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the last commit rides one sync.
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**Replay** decodes payloads straight into engine-owned values — no VM heap
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involved, boot cannot depend on a VM existing — and rows re-enter through
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the choke-point row API, so Task 4's indexes rebuild for free. A torn tail
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(short record, bad CRC, missing mark, zero length) ends the intact prefix:
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everything from the tear on is dropped whole, and `wo_wal_open` positions
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its write offset AT the tear so the next commit overwrites it. A record that
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CRC-passes but does not decode is corruption, not a tear — replay fails
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loudly. A missing file is a fresh boot, not an error. After replay each
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table's `next_id` sits past every replayed id this shard owns.
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**Oracle:** `wo_wal_check(path)` walks a file with no engine and reports the
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intact record count and prefix end — the crash battery's verifier
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(`runtime/test/test_wal.c`: five rounds of insert/commit/ack-over-pipe with
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SIGKILL mid-stream; every acked row present and exact after replay).
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## Still to come in this document
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- **Task 3**: the `insert` statement's builtin ids (appended to
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`00-wob-format.md`'s builtin table) and execution contract.
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- **Task 4**: secondary-index format, `@unique` trap code.
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- **Task 5**: the select subset, update record semantics, and its builtins.
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