Feature flags

The engine has no required features — the default build pulls in only redb and is #![forbid(unsafe_code)]. Two optional cargo features exist, both OFF by default so the dependency-minimal default build and the WASM size budget stay contracts:

[dependencies]
corvid = { git = "https://github.com/corvid-db/corvid", features = ["zstd"] }

zstd — transparent document compression

With the feature on, values in user collections whose encoding is ≥ 1 KiB are compressed (zstd level 3) when written and decompressed on every read path — queries, scans, paging, indexes, TTL, edges, dump/load, and backup all behave identically, just smaller on disk.

• Stored rows are self-describing (a reserved leading marker byte 0xFF no value encoding can produce), so databases written by default (feature-off) builds read fine under a feature-on build, and dump output is format-stable v2 either way.
• Incompressible values are stored raw (never larger). The known tax: a ≥1 KiB random value pays the compression attempt (~0.85 µs/KiB) and is stored raw anyway.
• Engine-internal __ namespaces (indexes, edges, TTL) stay raw.

Measured ratios (deterministic corpora, exact byte counts):

Document	Stored	Ratio
Structured text map, 50,975 B	4,242 B	8.3% (12×)
f32 vector array (smooth sin values), 16k dims	59,933 B	91.4% (~1.1×)
Random bytes, 64 KiB	raw	—

The honest headline: vector payloads barely compress — IEEE-754 mantissas are near-full entropy even for smooth sequences. zstd is a text/document play; the vector footprint levers are quantization (Binary/Scalar/PQ).

Per-op overhead (8 KiB document, insert/get): ~+4.9 µs/write, ~+2.6 µs/read for compressible text; raw rows read at parity.

Portability caveat: backups are physical copies — a backup written by an ON build fails per-row Decode under an OFF binary. dump/load carries raw encodings either way and is the migration path between feature builds.

tracing — structured instrumentation

corvid = { features = ["tracing"] }

Structured events at the engine’s load-bearing points, via the tracing facade (trimmed: span!/event! only) — attach any tracing-compatible subscriber; events carry target = "corvid". No public API change; when the feature is off, every call site compiles to nothing through a private telemetry shim (CI asserts the default and WASM dependency graphs never contain tracing).

Instrumented at per-operation/per-page granularity (never per-document) — the full inventory is on the observability page.

Next: observability.