`MemoryConfig::quantized_index` stores the HNSW index's own copy of the
embeddings as i8 rather than f32. At 100k x 384 that takes the index from
266 to 123 MiB and the whole reopened store from 399 to 256 MiB — 2.72x
to 1.74x the raw vectors, the largest remaining item in the footprint.
Quantised distances are approximate and `ef` cannot compensate, because
the loss is in the distances rather than in the graph: recall@10 tops out
at 0.967 against f32's 0.9995 and does not move between ef=128 and
ef=256. The store already holds the exact embeddings, though, so when the
index is quantised the query path re-scores the candidate pool against
them before fusion. That restores recall (0.9940 vs 0.9945 at ef=64) and
costs about 13% of QPS.
Off by default: it trades query speed for memory and which side is worth
more depends on the deployment. The flag is persisted in `/meta`, so a
reopened store does not silently revert to four times the index memory,
and the sidecar graph is rehydrated into the configured storage.
Also on the CLI as `create --quantized-index`.
Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
- HDF5Memory::create/open take an exclusive advisory lock on <store>.h5.lock
(std File::try_lock, no new dependency). The store lives in memory and is
rewritten wholesale at each checkpoint, so two handles on one store used to
silently destroy each other's data; a second writer now gets
MemoryError::Locked. The OS drops the lock with the descriptor, so a crash
never leaves a stale lock. Acquisition retries for ~250 ms to absorb a
previous owner that is mid-teardown; AsyncHDF5Memory::shutdown releases the
lock once its writer task has stopped.
- HDF5Memory::open_read_only: a lock-free, point-in-time view (checkpoint +
current WAL contents, replayed in memory) that never writes — it does not
repair, upgrade or move the WAL, and anything that would persist returns an
error. The CLI's recall/stats/agents-md/export use it, so a store can be
inspected while an agent has it open. Tests that reopened a store purely to
verify on-disk state now use it.
- open() no longer fails on a WAL that cannot possibly be replayed (torn
header, bad magic): it is moved to <store>.h5.wal.corrupt-<ts>, reported via
HDF5Memory::quarantined_wal(), and the healthy .h5 opens from its last
checkpoint. A well-formed header with an unknown version still fails and is
left untouched — most likely a newer build's WAL, which must not be
discarded.
Co-Authored-By: Claude Fable 5.1 <[email protected]>
