Andrey Antukh 70b8c898a1 ✨ Stabilize fragmented file data across snapshots and GC
Snapshots, automatic and user, now store pointer-based rows that share
fragments with the live file instead of duplicating page content.
`get-file-snapshot` resolves those pointers on the server so version
previews keep rendering plain data, and `restore!` reuses the shared
rows. Export still materializes (the package carries no fragments) and
import regenerates them.

`file-gc` treats the main file and every unpurged snapshot as liveness
roots, reads the file unrealized, and reattaches the original pointer
wherever the cleaned value is unchanged, so a pass over an untouched
file writes no fragments and a pass over an edited file keeps the ids
of the pages it did not touch. Snapshot creation and the restore
backup take the file row `FOR SHARE`, which serializes them with the
pass and closes the race that let a new snapshot reference fragments
the pass was about to mark.

All backend pointer bindings go through the `fdata/with-pointers`,
`with-tracked`, `with-tracked-pointers` and `with-untracked` macros.
The loader reads fragments a previous pass marked until `objects-gc`
purges them, and the frontend fails loudly with retry instead of
dropping an unresolved fragment.

Review fixes in this branch: the automatic snapshot attaches before
pending migrations, `realize-pointers` is the single verb,
`reattach-unchanged` takes the identity fast path, the restore guard
takes its revn from the backup read, and `PointerMap.withMeta`
generates a fresh id when metadata changes.

Tests cover both snapshot writers (red without the lock), snapshot
sharing and pin release through the real delete and purge paths,
reattach against orphan marking, preview after offload, the pointer
binding contracts and the with-meta id change.

Closes #12410

AI-assisted-by: muse-spark-1.3-contributor
AI-assisted-by: deepseek-v4.1-flash

♻️ Pin no-churn behavior for untouched pages

Pin the behavior the churn verification measured: a save keeps the
fragment id of every page it does not touch, with a page of eleven keys
(PersistentHashMap), a 46-shape objects map and a nine-page index (hash
map). Also pin the mixed case: a data-level objects-map flip rewrites
the old pointer pages once and the next save keeps the new ids.

The memory records the identity rule behind it: re-assoc with the same
value returns the same map in array and hash maps alike.

Closes #12410

AI-assisted-by: deepseek-v4.1-flash

⚡ Stop loading untouched pages when enabling objects-map

`enable-objects-map` wrapped every page on every save, and reading a
page's objects forced its PointerMap to load the fragment. A save of
one page in a seven-page file therefore made seven fragment reads.

Skip unloaded pointers: their fragment was already wrapped by the
encode-file that wrote it, so loading it only to wrap it again is a
no-op. The save now loads only the pages it edits. A page with a plain
fragment (a data-level feature flip) keeps its plain fragment until it
is first loaded or edited; a migration that enables the feature must
rewrite the data itself.

Cover the change with load-count tests for save and restore, update the
flip test to the new contract, and drop the stale restore comment.

Closes #12410

AI-assisted-by: deepseek-v4.1-flash

⚡ Keep page fragment ids through pending migrations

Applying a pending migration on read realized the file, ran the
migration and persisted it again; the persist wrapped every plain page
in a new PointerMap, so every page got a new fragment id even when the
migration did not change it. That leaves the fragment cache cold and
rewrites every fragment on the first read after a deploy.

Capture the original pointers before realizing, reattach the unchanged
positions after migrating (same value comparison file-gc already uses),
persist the reattached file and return the realized one: the read
contract is plain data. Read-only connections skip the persist and the
reattach. A migration that adds objects-map skips the reattach so the
pages get wrapped.

Move the three helpers to fdata so file-gc and the migration path share
them, and cover the path with a real 0031 migration test: the unchanged
page keeps its id, the changed page gets a new one, the caller gets
realized data and a second read does not migrate again.

Closes #12410

AI-assisted-by: deepseek-v4.1-flash
2026-10-23 17:20:13 +02:00
..
2026-10-07 10:41:29 +02:00
2024-05-29 19:05:04 +02:00