Local Models / Transformers ​

LMQL relies on a two-process architecture: The inference process (long-running) loads the model and provides an inference API, and the interpreter process (short-lived) executes your LMQL program.

This architecture is advantageous for locally-hosted models, as the model loading time can be quite long or the required GPU hardware might not even be available on the client machine.

This chapter first discusses how to use of the two-process inference API, and then presents an alternative on how to leverage In-Process Model Loading, which avoids the need for a separate server process within the same architecture.

Prerequisites Before using a local model, make sure you installed LMQL via pip install lmql[hf]. This ensures the dependencies for running local models are installed. This requirement also applies to llama.cpp, as LMQL still relies on HuggingFace transformers for tokenization.

Then, to start an LMQL inference server, e.g. for the gpt2-medium model, you can run the following command:

lmql serve-model gpt2-medium --cuda

--cuda will load the model on the GPU, if available. If multiple GPUs are available, the model will be distributed across all GPUs. To run with CPU inference, omit the --cuda flag. If you only want to use a specific GPU, you can specify the CUDA_VISIBLE_DEVICES environment variable, e.g. CUDA_VISIBLE_DEVICES=0 lmql serve-model gpt2-medium.

By default, this exposes an LMQL/LMTP inference API on port 8080. When serving a model remotely, make sure to tunnel/forward the port to your client machine. Now, when executing an LMQL query in the playground or via the CLI, you can simply specify e.g. gpt2-medium, and the runtime will automatically connect to the model server running on port 8080 to obtain model-generated text.

Configuration ​

Endpoint and Port By default, models will be served via port 8080. To change this, you can specify the port via the --port option of the lmql serve-model command. On the client side, to connect to a model server running on a different port, you can specify the port when constructing an lmql.model object:

lmql.model("gpt2", endpoint="localhost:9999")

Model Configuration To load a model with custom quantization preferences or other Transformers arguments, you can specify additional arguments when running the lmql serve-model command. For this, you can provide arbitrary arguments that will directly be passed to the underyling AutoModelForCausalLM.from_pretrained(...) function, as documented in the Transformers documentation.

For example, to set trust_remote_code to True with the from_pretrained function, run the following:

lmql serve-model gpt2-medium --cuda --port 9999 --trust_remote_code True

Alternatively, you can also start to serve a model directly from within a Python environment, by running lmql.serve("gpt2-medium", cuda=True, port=9999, trust_remote_code=True). Just as with the CLI, standard transformers arguments are passed through, to the AutoModel.from_pretrained function.

In-Process Models ​

If you would like to load the model in-process, without having to execute a separate lmql serve-model command, you can do so by instantiating a custom lmql.model object with local: as part of the model name. For example, to load the gpt2-medium model in-process, run the following command:

argmax "Hello[WHO]" from lmql.model("local:gpt2")

Note however, that this will load the model on each restart of the LMQL process, which can incur a significant overhead.

If you want more control over model loading and configuration, you can pass additional arguments to lmql.model(...), as demonstrated below.

lmql.model("local:gpt2", cuda=True)