Clear the KV cache

The clear interface is defined as the following:

clear(instance_id: str, location: str) -> event_id: str, num_tokens: int

The function removes the KV cache stored at location for the specified instance_id. It returns an event_id and the number of tokens scheduled for clearing.

Example usage:

First, create a yaml file example.yaml to configure the lmcache instance:

chunk_size: 256
local_cpu: True
max_local_cpu_size: 5

# cache controller configurations
enable_controller: True
lmcache_instance_id: "lmcache_default_instance"
controller_url: "localhost:9001"
distributed_url: "localhost:8002"
lmcache_worker_port: 8001

Start the vllm/lmcache instance at port 8000:

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"}'

Start the lmcache controller at port 9000 and the monitor at port 9001:

lmcache_controller --host localhost --port 9000 --monitor-port 9001

Send a request to vllm:

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
      }'

Clear the KV cache in the system:

curl -X POST http://localhost:9000/clear \
  -H "Content-Type: application/json" \
  -d '{
        "instance_id": "lmcache_default_instance",
        "location": "LocalCPUBackend"
      }'

The controller responds with a message similar to:

{"event_id": "xxx", "num_tokens": 12}

This indicates that the KV cache for 12 tokens has been scheduled for clearing. We can verify the cache has been cleared by performing a lookup:

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]
      }'

The lookup should return an empty result, confirming that the KV cache has been cleared for the given tokens.