A multi-object delete spans many keys that route to different owner filers. The
gateway groups keys by owner and sends one batch per owner; the filer applies
each transaction under its own per-path lock, independent of the others.
A failed transaction (precondition or mutation error) is reported in its own
response without aborting the rest, matching S3 multi-object semantics where
each key succeeds or fails on its own. There is no cross-key atomicity, which S3
batch delete does not require.
Deleting a specific version that happens to be the latest needs the new latest
re-derived from the remaining versions, and that scan must run under the same
lock as the delete. The gateway can't do it atomically across RPCs.
Add a RECOMPUTE_LATEST mutation: it scans a directory under the transaction
lock, picks the child that sorts last (descending) or first by name, copies the
mapped extended keys from it into a pointer entry, and stores its name under
name_to_key. An empty directory clears the pointer keys. The filer stays
mechanical and S3-agnostic: the caller, which knows the versioning scheme,
supplies the sort direction and the key mappings. A missing pointer entry is a
no-op, so a replayed transaction is idempotent.
A versioned object write touches several entries that must change together: the
main object, a delete marker or version file, and the latest pointer on the
.versions directory. Holding a distributed lock across separate RPCs to do this
is what the per-path lock was meant to replace, but a single CreateEntry only
covers one entry.
Add ObjectTransaction: a request carries a lock_key (the object path), an
optional WriteCondition, and an ordered list of mutations (PUT / DELETE /
PATCH_EXTENDED). The filer holds the per-path lock on lock_key for the whole
call, checks the condition against the entry at lock_key, then applies the
mutations in order. Callers route the object's writes to its owner filer so the
lock is authoritative across all of the object's entries.
DELETE and PATCH of an absent entry are no-ops, so a replayed transaction is
idempotent. PUT entries are metadata-scoped; data-bearing writes (chunks) are
written before the transaction, as today.
Chris Lu