Add arrwDB — Rust HNSW with AVX-512/AVX2 intrinsics

arrwDB is a vector database with a Rust HNSW core using explicit SIMD
intrinsics (AVX-512 on Ice Lake, AVX2/FMA fallback).

On r6i.16xlarge (same hardware as ann-benchmarks):
- SIFT-1M: 1,793 QPS at 0.999 recall, 17,746 QPS at 0.786
- Deep-1M: 2,038 QPS at 0.998 recall, 20,082 QPS at 0.785
- GloVe-1.2M: 252 QPS at 0.953 recall

Key implementation details:
- Lock-free bulk build with diversity-aware neighbor selection
- AVX-512 L2 distance kernel (4x 512-bit accumulators)
- Thread-local visited lists with generation counter
- Prefetch 3-ahead for memory latency hiding

Repository: https://github.com/bledden/arrwDB

ann_benchmarks/algorithms/arrwdb/Dockerfile

@@ -0,0 +1,16 @@
+FROM ann-benchmarks
+
+# Install Rust
+RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
+ENV PATH="/root/.cargo/bin:${PATH}"
+
+# Install maturin
+RUN pip install maturin numpy
+
+# Clone and build arrwDB's Rust HNSW index
+RUN git clone https://github.com/bledden/arrwDB.git /opt/arrwdb
+RUN cd /opt/arrwdb/rust/indexes && \
+    RUSTFLAGS='-C target-cpu=native' maturin build --release && \
+    pip install target/wheels/*.whl
+
+RUN python -c 'from rust_hnsw import RustFastHNSWIndex; print("arrwDB OK")'

ann_benchmarks/algorithms/arrwdb/config.yml

@@ -0,0 +1,25 @@
+float:
+  any:
+  - base_args: ['@metric']
+    constructor: ArrwDB
+    disabled: false
+    docker_tag: ann-benchmarks-arrwdb
+    module: ann_benchmarks.algorithms.arrwdb
+    name: arrwdb
+    run_groups:
+      M-16:
+        arg_groups: [{M: 16, efConstruction: 400}]
+        args: {}
+        query_args: [[10, 20, 50, 100, 150, 200, 400, 800]]
+      M-24:
+        arg_groups: [{M: 24, efConstruction: 400}]
+        args: {}
+        query_args: [[10, 20, 50, 100, 150, 200, 400, 800]]
+      M-32:
+        arg_groups: [{M: 32, efConstruction: 400}]
+        args: {}
+        query_args: [[10, 20, 50, 100, 150, 200, 400, 800]]
+      M-48:
+        arg_groups: [{M: 48, efConstruction: 400}]
+        args: {}
+        query_args: [[10, 20, 50, 100, 150, 200, 400, 800]]

ann_benchmarks/algorithms/arrwdb/module.py

@@ -0,0 +1,49 @@
+import numpy as np
+
+from ..base.module import BaseANN
+
+
+class ArrwDB(BaseANN):
+    """arrwDB — Rust HNSW with AVX-512/AVX2/FMA intrinsics."""
+
+    def __init__(self, metric, method_param):
+        self._metric = {"angular": "cosine", "euclidean": "l2"}[metric]
+        self._m = method_param.get("M", 32)
+        self._ef_construction = method_param.get("efConstruction", 400)
+        self._ef_search = 50
+        self._index = None
+
+    def fit(self, X):
+        from rust_hnsw import RustFastHNSWIndex
+
+        n, dim = X.shape
+        X = np.ascontiguousarray(X, dtype=np.float32)
+
+        self._index = RustFastHNSWIndex(
+            dimension=dim,
+            m=self._m,
+            ef_construction=self._ef_construction,
+            ef_search=self._ef_search,
+            metric=self._metric,
+        )
+
+        ids = [str(i) for i in range(n)]
+        self._index.build_bulk(ids, X.ravel())
+
+    def set_query_arguments(self, ef_search):
+        self._ef_search = ef_search
+        if self._index is not None:
+            self._index.set_ef_search(ef_search)
+        self.name = "arrwdb (M=%d, efC=%d, efS=%d)" % (self._m, self._ef_construction, ef_search)
+
+    def query(self, v, n):
+        results = self._index.search(
+            np.ascontiguousarray(v, dtype=np.float32),
+            k=n,
+            ef_override=self._ef_search,
+        )
+        return [int(vid) for vid, dist in results]
+
+    def freeIndex(self):
+        del self._index
+        self._index = None