Prerequisite 0 of docs/plan/derived-blobs.md. The zero-ref manifest
sweep read:
WHERE m.ref_count <= 0
OR NOT EXISTS (SELECT 1 FROM storage.files f
WHERE f.blob_hash = m.file_hash)
That OR hardcodes "storage.files is the only thing that can reference a
manifest". A thumbnail manifest held by storage.content_derived_blobs
has ref_count = 1, so the first clause is false — but no files row names
a thumbnail's Blob hash, so NOT EXISTS is true, the OR fires, and the
manifest is deleted, its chunks dereferenced and the bytes reaped on the
next sweep. Landing content_derived_blobs before this fix would destroy
the derived tier on the first GC run.
The second clause is not merely defensive: it is the ONLY reap path for
bulk deletes (user cascade, empty_trash), where the PG trigger touches
storage.blobs but never decrements the manifest and the per-file
cleanup_if_orphaned call is skipped. So the fix has to preserve that
role, not just add tables to the NOT EXISTS. It is now the union of
every registered manifest-level source.
Assembled once, not per sweep. An earlier cut of this change put a
format! inside the DELETE, which made the most dangerous statement in
the file unreadable, un-pasteable into psql, and injection-shaped even
though every input is &'static str. The statement is now built at
construction and stored on DedupService, so:
* the reap loop runs a fixed statement with no string work,
* the SQL string is stable, so prepared-statement cache keys are too,
* a golden test pins it byte-for-byte — a reviewer reads the SQL in
the test rather than mentally evaluating the registry,
* initialize() logs it at debug with the contributing source names,
recovering the "paste it into psql" property the literal had.
The registry is mandatory rather than Option. An empty registry makes
"nothing references it" vacuously true for every row, so the builder
panics instead of emitting a statement that would delete every manifest
in the database; DedupService::new always registers the two built-in
sources, so that panic is unreachable by construction. There is a test
for it.
Adds ref_exists_sql to the port, defaulting to (count) > 0 and
overridden by FilesReferenceSource with a real EXISTS. Without it the
reap predicate would have traded today's short-circuiting NOT EXISTS
for a COUNT(*) = 0 that scans every referrer — a regression precisely
on heavily-deduplicated blobs, which is what GC walks most.
fmt, clippy --all-features --all-targets, and the 11 affected unit
tests all clean.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Edouard Vanbelle
a68c938400