.. _lookup:

Lookup the KV cache
===================

.. warning::

   This page documents the behavior of LMCache's in-process mode (deprecated). Please consider using :doc:`LMCache MP mode </mp/index>` for better feature support and performance.


The ``lookup`` interface is defined as the following: 

.. code-block:: python

    lookup(tokens: List[int]) -> event_id: str, layout_info: Dict[str, Tuple[str, int]]

The function takes a list of tokens as input and returns event_id and a dictionary containing the layout information for each token.
The layout information is represented as a mapping between ``instance_id`` and a tuple of ``(location, matched_prefix_length)``.

Example usage:
---------------------------------------

First, we need a yaml file ``example.yaml`` to properly configure the lmcache instance:

.. code-block:: yaml

    chunk_size: 256
    local_cpu: True
    max_local_cpu_size: 5

    # cache controller configurations
    enable_controller: True
    lmcache_instance_id: "lmcache_default_instance"
    controller_pull_url: "localhost:9001"
    lmcache_worker_ports: 8001

    # Peer identifiers
    p2p_host: "localhost"
    p2p_init_ports: 8200

Second, we need to start the vllm/lmcache instance at port 8000:

.. code-block:: bash

    PYTHONHASHSEED=123 CUDA_VISIBLE_DEVICES=0 LMCACHE_CONFIG_FILE=example.yaml vllm serve meta-llama/Llama-3.1-8B-Instruct --max-model-len 4096  --gpu-memory-utilization 0.8 --port 8000 --kv-transfer-config '{"kv_connector":"LMCacheConnectorV1", "kv_role":"kv_both"}'

Third, we need to start the lmcache controller at port 9000 and the monitor at port 9001:

.. code-block:: bash

    PYTHONHASHSEED=123 lmcache_controller --host localhost --port 9000 --monitor-port 9001

Then we can send a request to vllm to see if it works properly:

.. code-block:: bash

    curl -X POST http://localhost:8000/v1/completions \
      -H "Content-Type: application/json" \
      -d '{
        "model": "meta-llama/Llama-3.1-8B-Instruct",
        "prompt": "Explain the significance of KV cache in language models.",
        "max_tokens": 10
      }'

Now we send a request to tokenize the prompt:

.. code-block:: bash

    curl -X POST http://localhost:8000/tokenize \
      -H "Content-Type: application/json" \
      -d '{
        "model": "meta-llama/Llama-3.1-8B-Instruct",
        "prompt": "Explain the significance of KV cache in language models."
      }'

We should be able to see token ids in response:

.. code-block:: text

    {"count":12,"max_model_len":4096,"tokens":[128000,849,21435,279,26431,315,85748,6636,304,4221,4211,13],"token_strs":null}

Finally, we can send a ``lookup`` request to the lmcache controller:

.. code-block:: bash

    curl -X POST http://localhost:9000/lookup \
      -H "Content-Type: application/json" \
      -d '{
        "tokens": [128000, 849, 21435, 279, 26431, 315, 85748, 6636, 304, 4221, 4211, 13]
      }'

We should be able to see the response like this:

.. code-block:: text

    {"event_id": "xxx", "lmcache_default_instance": ("LocalCPUBackend", 12)}

The field ``lmcache_default_instance`` shows the instance ID, followed by a tuple of ``(location, matched_prefix_length)`` indicating the cache location within that instance and matched prefix length. ``event_id`` is an identifier of the controller operation and can typically be ignored.