feat(filter): replace standard bloom with BuRR

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "coordinode-lsm-tree"
-description = "A K.I.S.S. implementation of log-structured merge trees (LSM-trees/LSMTs) — CoordiNode fork"
+description = "Embedded LSM-tree storage engine: BuRR filters, zstd dictionary compression, MVCC, range tombstones, merge operators, K/V separation, AES-256-GCM at rest."
 license = "Apache-2.0"
 version = "4.5.0"
 edition = "2024"
@@ -9,8 +9,19 @@ readme = "README.md"
 include = ["src/**/*", "build.rs", "LICENSE-APACHE", "README.md", "CHANGELOG.md"]
 repository = "https://github.com/structured-world/coordinode-lsm-tree"
 homepage = "https://github.com/structured-world/coordinode-lsm-tree"
-keywords = ["lsm-tree", "storage", "database", "coordinode", "key-value"]
-categories = ["data-structures", "database-implementations"]
+documentation = "https://docs.rs/coordinode-lsm-tree"
+keywords = ["lsm-tree", "storage", "database", "embedded", "key-value"]
+categories = ["data-structures", "database-implementations", "filesystem", "compression"]
+
+[package.metadata.docs.rs]
+# Build the docs.rs page with every feature enabled so the rendered
+# crate page exposes the full public API surface (zstd dictionary
+# compression, encryption, io-uring, bytes integration, metrics,
+# ribbon-serde). cfg(docsrs) is set so #[cfg_attr(docsrs, ...)] items
+# render their feature/availability badges.
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
+targets = ["x86_64-unknown-linux-gnu"]
 
 [lib]
 name = "lsm_tree"
@@ -20,11 +31,26 @@ path = "src/lib.rs"
 default = []
 io-uring = ["dep:io-uring"]
 lz4 = ["dep:lz4_flex"]
+# The previous `zstd-pure = ["zstd"]` alias was removed. It was
+# documented as deprecated when there were two candidate zstd backends
+# on the roadmap; only structured-zstd remains, so the alias serves no
+# purpose and is dropped per the standard deprecation lifecycle. The
+# removal is signalled to release tooling as a breaking change via the
+# conventional `!` markers on this PR's breaking commits (BuRR filter
+# wire format, V5 manifest gate); release-plz raises the crate's major
+# version on the next release tag accordingly.
 zstd = ["dep:structured-zstd"]
-zstd-pure = ["zstd"]
 encryption = ["dep:aes-gcm", "dep:rand_chacha"]
 bytes_1 = ["dep:bytes"]
 metrics = []
+# Vendored Ribbon filter retains its `#[cfg(feature = "ribbon-serde")]`
+# guards (renamed from upstream's bare `serde` feature to avoid clashing
+# with any future top-level serde feature in this crate). We do not
+# consume the serde repr from inside this crate — the BuRR on-disk
+# format is byteorder-encoded — but the feature wires `serde` as an
+# optional dep so `--all-features` builds and a future extraction back
+# into a standalone crate compile cleanly.
+ribbon-serde = ["dep:serde"]
 
 [dependencies]
 bytes = { version = "1", optional = true }
@@ -38,6 +64,9 @@ structured-zstd = { version = "0.0.21", optional = true, default-features = fals
 quick_cache = { version = "0.6.16", default-features = false, features = [] }
 rustc-hash = "2.1.1"
 self_cell = "1.2.0"
+# Optional — only pulled in by the vendored Ribbon filter under the
+# `ribbon-serde` feature flag (off by default).
+serde = { version = "1", optional = true, features = ["derive"] }
 sfa = "~1.0.0"
 tempfile = "3.20.0"
 varint-rs = "2.2.0"
@@ -65,6 +94,9 @@ fs_extra = "1.3.0"
 nanoid = "0.5.0"
 proptest = "1"
 rand = "0.10.1"
+# Used by the vendored ribbon-filter's #[cfg(feature = "ribbon-serde")]
+# round-trip tests. Dev-only; production code does not depend on it.
+serde_json = "1"
 strum = { version = "0.28.0", features = ["derive"] }
 test-log = "0.2.18"
 

README.md

@@ -1,6 +1,4 @@
-<p align="center">
-  <img src="/logo.png" height="160">
-</p>
+# coordinode-lsm-tree
 
 [![CI](https://github.com/structured-world/coordinode-lsm-tree/actions/workflows/coordinode-ci.yml/badge.svg)](https://github.com/structured-world/coordinode-lsm-tree/actions/workflows/coordinode-ci.yml)
 [![codecov](https://codecov.io/gh/structured-world/coordinode-lsm-tree/graph/badge.svg)](https://codecov.io/gh/structured-world/coordinode-lsm-tree)
@@ -11,107 +9,106 @@
 [![dependency status](https://deps.rs/repo/github/structured-world/coordinode-lsm-tree/status.svg)](https://deps.rs/repo/github/structured-world/coordinode-lsm-tree)
 [![License](https://img.shields.io/badge/license-Apache--2.0-blue)](#license)
 
-> LSM-tree engine for [CoordiNode](https://github.com/structured-world/coordinode), maintained by [Structured World Foundation](https://sw.foundation).
-> Derivative work of [fjall-rs/lsm-tree](https://github.com/fjall-rs/lsm-tree), developed independently with diverging features: zstd dictionary compression, custom sequence number generators, multi_get (batch-optimized), PinnableSlice zero-copy reads, WriteBatch seqno-grouped batch writes with caller-controlled atomic visibility, intra-L0 compaction, and security hardening.
+LSM-tree storage engine in Rust. Embedded library; provides keyed point reads, prefix and range scans, MVCC snapshots, compaction, and a block cache. No write-ahead log — durability is the caller's responsibility. Built for [CoordiNode](https://github.com/structured-world/coordinode); usable standalone.
 
-> [!IMPORTANT]
-> This fork now introduces a fork-specific **disk format V4** compatibility boundary.
-> `V4` is a breaking on-disk change relative to `V3` because the fork persists new semantics such as range tombstones and merge operands.
-> New code may continue reading supported `V3` databases, but databases written with these `V4` semantics must not be opened by older `V3` binaries.
+## Status
 
-A K.I.S.S. implementation of log-structured merge trees (LSM-trees/LSMTs) in Rust.
+On-disk format version **V5**. V5 introduces a wire-format break for filter blocks (BuRR replaces Bloom); V3 and V4 databases are not readable by this version and vice versa. Versioning is single-monotonic — every breaking format change bumps to the next version with explicit migration notes.
 
-> [!NOTE]
-> This crate only provides a primitive LSM-tree, not a full storage engine.
-> For example, it does not ship with a write-ahead log.
-> You probably want to use https://github.com/fjall-rs/fjall instead.
+## Features
 
-## About
+### Read path
 
-This is the most feature-rich LSM-tree implementation in Rust! It features:
+- Point reads via `get` / `multi_get` (batch-optimized).
+- `PinnableSlice` for zero-copy reads.
+- `BurrFilter` AMQ filter (Bumped Ribbon Retrieval, Walzer & Dillinger 2022): ~1% memory overhead vs the information-theoretic minimum — ~30% smaller filter blocks than a same-FPR Bloom filter, or ~10× tighter FPR at the same memory budget. Used for both per-key and per-prefix membership checks.
+- Forward and reverse range / prefix iteration.
+- Block cache with size cap.
+- File-descriptor cache to bound `fopen` syscalls.
 
-- Thread-safe `BTreeMap`-like API
-- Mostly [safe](./UNSAFE.md) & 100% stable Rust
-- Block-based tables with compression support & prefix truncation
-  - Optional block hash indexes in data blocks for faster point lookups [[3]](#footnotes)
-  - Per-level filter/index block pinning configuration
-- Range & prefix searching with forward and reverse iteration
-- Block caching to keep hot data in memory
-- File descriptor caching with upper bound to reduce `fopen` syscalls
-- *AMQ* filters (currently Bloom filters) to improve point lookup performance
-- Multi-versioning of KVs, enabling snapshot reads
-- Optionally partitioned block index & filters for better cache efficiency [[1]](#footnotes)
-- Leveled and FIFO compaction
-- Optional key-value separation for large value workloads [[2]](#footnotes), with automatic garbage collection
-- Single deletion tombstones ("weak" deletion)
-- Optional compaction filters to run custom logic during compactions
+### Write path
 
-Keys are limited to 65536 bytes, values are limited to 2^32 bytes.
-As is normal with any kind of storage engine, larger keys and values have a bigger performance impact.
+- `WriteBatch` with seqno-grouped batch writes — caller-controlled atomic visibility.
+- Single deletion tombstones (`remove_weak`).
+- Range tombstones (`delete_range` / `delete_prefix`).
+- Merge operators for commutative LSM operations.
+- Optional key-value separation (BlobTree) for large-value workloads with automatic garbage collection.
 
-## Feature flags
-
-### lz4
+### Compaction
 
-Allows using `LZ4` compression, powered by [`lz4_flex`](https://github.com/PSeitz/lz4_flex).
+- Leveled, size-tiered, dynamic-leveled, and FIFO strategies.
+- Intra-L0 compaction for overlapping runs.
+- Major compaction (full force flush + merge).
+- Optional compaction filters for custom logic during compactions.
+- Merge-aware compaction resolves operands lazily.
 
-*Disabled by default.*
+### Storage & encoding
 
-### zstd
+- Block-based tables with optional compression (none / LZ4 / Zstd) and prefix truncation.
+- Per-table data block size policy and per-table compression policy.
+- Optional **zstd dictionary compression** — trained per-table or per-column for small (4-64 KiB) blocks and blob files.
+- Optional **block-level encryption at rest** — AES-256-GCM, key supplied by caller.
+- Optional per-table block hash indexes for faster point lookups [[3]](#footnotes).
+- Optional partitioned block index & filters for better cache efficiency [[1]](#footnotes).
+- Per-level filter/index block pinning configuration.
 
-Allows using `Zstd` compression via a pure Rust implementation, powered by
-[`structured-zstd`](https://github.com/structured-world/structured-zstd) (managed fork of ruzstd).
-Requires no C compiler or system libraries — compiles with `cargo build` alone.
-Supports both regular zstd (`CompressionType::Zstd`) and dictionary compression
-(`CompressionType::ZstdDict`) for improved ratios on small table blocks (4–64 KiB)
-and blob files.
+### Concurrency & API
 
-**Current limitations:**
-- Decompression throughput is ~2–3.5× slower than the C reference implementation
+- Thread-safe `BTreeMap`-like API.
+- `SequenceNumberGenerator` trait — pluggable seqno source.
+- Custom `UserComparator` for non-lexicographic ordering.
+- MVCC: snapshot reads at a chosen `SeqNo`.
 
-*Disabled by default.*
+### Internals
 
-### zstd-pure
+- 100% stable Rust, MSRV 1.92.
+- No FFI: zstd via [`structured-zstd`](https://github.com/structured-world/structured-zstd) (pure-Rust), LZ4 via `lz4_flex`, AES via `aes-gcm`.
+- Pluggable `Fs` trait — back the engine on the standard filesystem, on `io_uring`, on an in-memory `MemFs`, or on a custom implementation.
+- Pluggable `CompressionProvider` for third-party codecs.
 
-Deprecated alias for `zstd`. Enabling `zstd-pure` is equivalent to enabling `zstd`
-and will be removed in a future release.
+## Limits
 
-*Disabled by default.*
+- Keys: up to 65 536 bytes.
+- Values: up to 2³² bytes.
+- Larger keys and values carry a proportional performance cost.
 
-### bytes
+## Feature flags
 
-Uses [`bytes`](https://github.com/tokio-rs/bytes) as the underlying `Slice` type.
+All optional, all off by default. The default build is the minimal core (no compression, no encryption, std filesystem). Every flag below is gated because it pulls in extra dependencies or runtime overhead.
 
-*Disabled by default.*
+| Flag | Pulls in | Enable when |
+|---|---|---|
+| `lz4` | [`lz4_flex`](https://github.com/PSeitz/lz4_flex) | Block compression wanted, decompression latency matters more than ratio. |
+| `zstd` | [`structured-zstd`](https://github.com/structured-world/structured-zstd) (pure-Rust, no FFI) | Block compression wanted, ratio matters more than absolute decompression speed. Supports `CompressionType::Zstd` and dictionary-mode `CompressionType::ZstdDict`. Decompression is ~2-3.5× slower than C reference. |
+| `encryption` | `aes-gcm`, `rand_chacha` | AES-256-GCM block encryption at rest. Keys are caller-managed. |
+| `io-uring` (linux only) | [`io-uring`](https://github.com/tokio-rs/io-uring) | I/O-bound workload on a modern Linux kernel — adds an `io_uring` `Fs` backend. |
+| `bytes_1` | [`bytes`](https://github.com/tokio-rs/bytes) | Consumer already speaks `bytes::Bytes` (tokio/hyper/tonic stack) and wants zero-copy interop with engine slices. |
+| `metrics` | — | Production observability or profiling. Compiles in atomic counters around block I/O, filter probes, compaction, and cache hit rates (`tree.metrics()`). Small but non-zero hot-path cost. |
+| `ribbon-serde` | `serde` | Snapshotting the internal `RibbonFilterRepr` for debugging or out-of-band transport. Not used by the on-disk format. |
 
 ## Benchmarks
 
-CI runs [`db_bench`](tools/db_bench) on every push to `main` and on pull requests.
-Results from `main` are published to the
-[benchmark dashboard](https://structured-world.github.io/coordinode-lsm-tree/dev/bench/).
-PRs that regress performance by >15% trigger an alert; >25% regression fails CI.
+CI runs [`db_bench`](tools/db_bench) on every push to `main` and on pull requests. Results from `main` are published to the [benchmark dashboard](https://structured-world.github.io/coordinode-lsm-tree/dev/bench/). PRs regressing performance by more than 15% trigger an alert; more than 25% fails CI.
 
-Flamegraphs are generated on every merge to `main` using instrumented `db_bench` runs
-and published under `flamegraphs/<commit-sha>/flamegraph.svg` on
-[gh-pages](https://structured-world.github.io/coordinode-lsm-tree/).
+Flamegraphs are generated on every merge to `main` from instrumented `db_bench` runs and published under `flamegraphs/<commit-sha>/flamegraph.svg` on [gh-pages](https://structured-world.github.io/coordinode-lsm-tree/).
 
-To run Criterion microbenchmarks locally:
+Local Criterion microbenchmarks:
 
 ```bash
 cargo bench --features lz4
 ```
 
-To generate flamegraphs locally (requires the `flamegraph` feature):
+Local flamegraphs:
 
 ```bash
 cd tools/db_bench
 cargo run --release --features flamegraph -- \
   --benchmark all --num 100000 --flamegraph --skip-calibration
-# Folded stacks written to target/flamegraphs/all.folded
-# Render with: cargo install inferno && inferno-flamegraph target/flamegraphs/all.folded > flame.svg
+# Folded stacks: target/flamegraphs/all.folded
+# Render: cargo install inferno && inferno-flamegraph target/flamegraphs/all.folded > flame.svg
 ```
 
-## Support the Project
+## Support the project
 
 <div align="center">
 
@@ -121,13 +118,17 @@ USDT (TRC-20): `TFDsezHa1cBkoeZT5q2T49Wp66K8t2DmdA`
 
 </div>
 
+## Credits
+
+Originally created by Marvin Blum as part of [fjall-rs/lsm-tree](https://github.com/fjall-rs/lsm-tree); this codebase carries the original copyright (`Copyright (c) 2024-present, fjall-rs`). The vendored Ribbon filter (`src/table/filter/ribbon/`) is by [William Rågstad](https://github.com/WilliamRagstad) — see [`src/table/filter/ribbon/_vendored/`](src/table/filter/ribbon/_vendored/) for the upstream license texts.
+
 ## License
 
-All source code is licensed under Apache-2.0.
+All source code is licensed under [Apache-2.0](LICENSE-APACHE). Each first-party `.rs` file carries an `SPDX-License-Identifier: Apache-2.0` header alongside the original-author copyright and the maintainer copyright (Structured World Foundation). Contributions are accepted under the same license.
 
-All contributions are to be licensed as Apache-2.0.
+The vendored Ribbon filter (`src/table/filter/ribbon/`) keeps its upstream layout — it carries William Rågstad's per-module licensing commentary rather than per-file SPDX headers, plus the original `LICENSE-APACHE` and `LICENSE-MIT` preserved verbatim in `src/table/filter/ribbon/_vendored/`. The upstream crate is dual-licensed (`MIT OR Apache-2.0`); we redistribute the vendored copy only under the Apache-2.0 arm per Apache-2.0 §4.
 
-Originally derived from [fjall-rs/lsm-tree](https://github.com/fjall-rs/lsm-tree). Independently maintained by [Structured World Foundation](https://sw.foundation).
+Maintained by [Structured World Foundation](https://sw.foundation).
 
 ## Footnotes