dtlvnative

Provides Rust interfaces and prebuilt native dependencies for the Datalevin database. Rust applications use source crates backed by native release binaries. JVM applications use platform JARs containing the compiled native libraries and JavaCPP JNI bindings.

The native dependencies are:

• dlmdb a fork of LMDB key value storage library.
• usearch a vector indexing and similarity search library that is exposed directly for callers.
• llama.cpp built as a CPU-only GGUF runtime for embeddings and prompt-based text generation.
• dtlv wraps DLMDB. It implements Datalevin iterators, counters and samplers.

Rust crates

• dtlvnative provides Rust APIs for storage, vector search, and model operations, with managed native handles.
• dtlvnative-sys provides the raw native bindings and is included automatically by dtlvnative.

Add this to your Cargo.toml to enable all three native dependencies:

[dependencies]
dtlvnative = { version = "1.1.3", features = ["usearch", "llama"] }

Feature	Interface
dlmdb (default)	Environments, databases, transactions, and cursors for Datalevin's DLMDB fork
usearch	Vector indexing, filtered and exact search, serialization, and borrowed index views
llama	CPU embeddings, tokenization, text generation, summarization, and vision/OCR
full	All three interfaces

For storage alone, use dtlvnative = "1.1.3". Each feature also works with default-features = false, allowing vector or model operations without storage.

Rust native binaries are available for these targets:

Platform	Rust target
macOS ARM64	aarch64-apple-darwin
Linux x86-64 (glibc)	x86_64-unknown-linux-gnu
Linux ARM64 (glibc)	aarch64-unknown-linux-gnu
Windows x86-64 (MSVC)	x86_64-pc-windows-msvc

The crates ship Rust source and generated bindings. CI builds the native dependencies separately and attaches them to GitHub releases. dtlvnative-sys downloads the archives for the enabled features and verifies their SHA-256 checksums. Consumers need Rust, its platform linker, and curl for the initial download; native C/C++ compilation and libclang are unnecessary.

DLMDB links statically. USearch and llama use shared libraries; when deploying an application, copy those libraries and their bundled OpenMP runtime together and set DTLVNATIVE_RUNTIME_DIR to that directory. System runtime requirements, offline builds, and examples are covered in the Rust guide.

JVM packages

The following platforms are supported by the JVM packages:

• macosx-arm64
• freebsd-x86_64
• linux-arm64
• linux-x86_64
• windows-x86_64

The name of the released JAR is org.clojars.huahaiy/dtlvnative-PLATFORM, where PLATFORM is one of the above.

Vector support using usearch on Windows is experimental.

llama.cpp text + embedding

dtlvnative packages the CPU backend of llama.cpp with OpenMP enabled. The packaged native API now supports embedding models, decoder-only text models for prompt-based generation, and multimodal OCR with PaddleOCR-VL GGUF models.

Embedding API

Function	Description
dtlv_llama_embedder_create	Load a GGUF model and create an embedder
dtlv_llama_embedder_n_embd	Return the embedding dimension
dtlv_llama_embedder_n_ctx	Return the context size (max tokens)
dtlv_llama_token_count	Count tokens for a string without allocating
dtlv_llama_tokenize	Tokenize a string into a caller-owned int[] buffer
dtlv_llama_detokenize	Convert tokens back to a UTF-8 string
dtlv_llama_embed	Compute an embedding for a single string
dtlv_llama_embed_batch	Compute embeddings for multiple strings in one call
dtlv_llama_embedder_destroy	Free the embedder

The model must be a GGUF embedding model. The current smoke test uses multilingual-e5-small-Q8_0.gguf.

dtlv_llama_embedder_create takes model_path, n_ctx, n_batch, n_threads, and normalize. Pass 0 for n_ctx and n_batch to use model defaults. A non-zero normalize returns L2-normalized embeddings.

Single embedding

DTLV.dtlv_llama_embedder embedder = new DTLV.dtlv_llama_embedder();
int rc = DTLV.dtlv_llama_embedder_create(
        embedder,
        "multilingual-e5-small-Q8_0.gguf",
        0, 0, 4, 1);

int nEmbd = DTLV.dtlv_llama_embedder_n_embd(embedder);
float[] output = new float[nEmbd];
rc = DTLV.dtlv_llama_embed(embedder, "query: hello world", output, nEmbd);

DTLV.dtlv_llama_embedder_destroy(embedder);

Token counting and tokenization

// check token count before embedding
int nTokens = DTLV.dtlv_llama_token_count(embedder, text);
int maxTokens = DTLV.dtlv_llama_embedder_n_ctx(embedder);

// tokenize, truncate, detokenize
int[] tokens = new int[maxTokens];
int actual = DTLV.dtlv_llama_tokenize(embedder, text, tokens, maxTokens);
if (actual > maxTokens) {
    // truncate to fit
    actual = maxTokens;
}
byte[] buf = new byte[text.length() * 4];
int len = DTLV.dtlv_llama_detokenize(embedder, tokens, actual, buf, buf.length);
String truncated = new String(buf, 0, len, StandardCharsets.UTF_8);

Batch embedding

PointerPointer texts = new PointerPointer("query: hello", "query: world");
int nTexts = 2;
float[] output = new float[nTexts * nEmbd];
rc = DTLV.dtlv_llama_embed_batch(embedder, texts, nTexts, output, output.length);
// output[0..nEmbd-1] = embedding for "query: hello"
// output[nEmbd..2*nEmbd-1] = embedding for "query: world"

The Java test in src/java/datalevin/dtlvnative/Test.java will use target/embedding-models/multilingual-e5-small-Q8_0.gguf if present, fall back to a repository-root copy if present, and otherwise download the model from Hugging Face before running the embedding smoke test.

Text generation API

The text-generation API is aimed at decoder-only instruction models such as Qwen 3.5 0.8B Instruct in GGUF format.

Function	Description
dtlv_llama_generator_create	Load a GGUF decoder-only text model
dtlv_llama_generator_n_ctx	Return the context size
dtlv_llama_generator_token_count	Count tokens for a prompt/document
dtlv_llama_generate	Generate text for a raw prompt
dtlv_llama_summarize	Build a summarization prompt and generate a summary
dtlv_llama_generator_destroy	Free the generator

dtlv_llama_generate and dtlv_llama_summarize return the number of UTF-8 bytes written to the caller-owned output buffer. When n_predict <= 0, they default to a 128-token generation budget. Prompt text that exceeds the context size is automatically truncated to the leading tokens that fit.

DTLV.dtlv_llama_generator generator = new DTLV.dtlv_llama_generator();
int rc = DTLV.dtlv_llama_generator_create(
        generator,
        "Qwen3.5-0.8B-Instruct-Q4_K_M.gguf",
        2048, 0, 4);

byte[] output = new byte[8192];
int len = DTLV.dtlv_llama_summarize(
        generator,
        "Datalevin embeds data locally and can pair vector search with LMDB-backed storage.",
        128,
        output,
        output.length);

String summary = new String(output, 0, len, StandardCharsets.UTF_8);
DTLV.dtlv_llama_generator_destroy(generator);

If you want to supply your own instruction prompt instead of the built-in summary helper, call dtlv_llama_generate directly.

Vision / OCR API

The vision API is aimed at multimodal GGUF models with a matching projector GGUF, such as PaddleOCR-VL-1.5-GGUF.

Function	Description
dtlv_llama_vision_generator_create	Load a multimodal text GGUF and matching mmproj GGUF
dtlv_llama_vision_generator_n_ctx	Return the context size
dtlv_llama_vision_generate	Generate text for a single image plus prompt
dtlv_llama_ocr	Run OCR with the built-in OCR: prompt
dtlv_llama_vision_generator_destroy	Free the vision generator

dtlv_llama_vision_generator_create takes model_path, mmproj_path, n_ctx, n_batch, n_threads, image_min_tokens, and image_max_tokens. Pass 0 for the numeric tuning parameters to keep the model defaults. The runtime is CPU-only in this package.

dtlv_llama_vision_generate and dtlv_llama_ocr return the number of UTF-8 bytes written to the caller-owned output buffer. The image prompt is single image only. If the prompt passed to dtlv_llama_vision_generate does not contain the multimodal marker, the native layer prepends it automatically.

DTLV.dtlv_llama_vision_generator generator = new DTLV.dtlv_llama_vision_generator();
int rc = DTLV.dtlv_llama_vision_generator_create(
        generator,
        "PaddleOCR-VL-1.5.gguf",
        "PaddleOCR-VL-1.5-mmproj.gguf",
        0, 0, 4, 0, 0);

byte[] output = new byte[8192];
int len = DTLV.dtlv_llama_ocr(
        generator,
        "page.png",
        16,
        output,
        output.length);

String text = new String(output, 0, len, StandardCharsets.UTF_8);
DTLV.dtlv_llama_vision_generator_destroy(generator);

Local llama smoke test

To refresh the JavaCPP platform libraries and run the local llama smoke tests with a real decoder model:

script/test-llama-summarization --text-model=target/text-models/qwen2.5-0.5b-instruct-q5_k_m.gguf

The script runs Test.java with --llama-only, so it covers both the llama embedding smoke test and the summarization flow. If you prefer, set DTLV_TEXT_MODEL_PATH=/abs/path/model.gguf instead of passing --text-model.

OCR smoke test

To refresh the JavaCPP platform libraries and run only the PaddleOCR-VL smoke test:

script/test-llama-ocr \
  --vision-model=/path/to/PaddleOCR-VL-1.5.gguf \
  --vision-mmproj=/path/to/PaddleOCR-VL-1.5-mmproj.gguf \
  --ocr-image=/path/to/image.png \
  --ocr-n-predict=16

The OCR script runs Test.java with --ocr-only, so it skips LMDB, usearch, embedding, and summarization. It also prints the extracted OCR text. You can set DTLV_VISION_MODEL_PATH, DTLV_VISION_MMPROJ_PATH, DTLV_OCR_IMAGE_PATH, and DTLV_OCR_N_PREDICT instead of passing the flags explicitly.

For CPU-only smoke tests, keep --ocr-n-predict small. 16 is a practical default for checking that OCR works end to end. Large document images are much slower than small or resized inputs, so for quick validation it helps to reduce the longest edge to around 512 pixels first.

Additional dependencies

The shared libraries in the JVM packages depend on some system libraries.

• libc
• libmvec
• libomp or libgomp

We bundle libomp in the Jar. However, on systems that the bundled library is not working, or libc is not available, you will have to install them yourself. For example, on Ubuntu/Debian, apt install libgomp1, or apt install gcc-12 g++-12; on MacOS, brew install libomp libllvm

License

Copyright © 2021-2026 Huahai Yang

This program and the accompanying materials are made available under the terms of the Eclipse Public License 2.0 which is available at http://www.eclipse.org/legal/epl-2.0.

This Source Code may also be made available under the following Secondary Licenses when the conditions for such availability set forth in the Eclipse Public License, v. 2.0 are satisfied: GNU General Public License as published by the Free Software Foundation, either version 2 of the License, or (at your option) any later version, with the GNU Classpath Exception which is available at https://www.gnu.org/software/classpath/license.html.