> ## Documentation Index
> Fetch the complete documentation index at: https://ultrarag.openbmb.cn/llms.txt
> Use this file to discover all available pages before exploring further.

# Reranker

## `reranker_init`

**Signature**

```python theme={null}
async def reranker_init(
    model_name_or_path: str,
    backend_configs: Dict[str, Any],
    batch_size: int,
    gpu_ids: Optional[object] = None,
    backend: str = "infinity",
) -> None
```

**Function**

* Initializes reranker backend and model.

***

## `reranker_rerank`

**Signature**

```python theme={null}
async def reranker_rerank(
    query_list: List[str],
    passages_list: List[List[str]],
    top_k: int = 5,
    query_instruction: str = "",
) -> Dict[str, List[Any]]
```

**Function**

* **Reranks** candidate passages:

**Output Format (JSON)**

```json theme={null}
{
  "rerank_psg": [
    ["best passage for q0", "..."],
    ["best passage for q1", "..."]
  ]
}
```

***

## Configuration

```yaml servers/reranker/parameter.yaml icon="https://mintcdn.com/ultrarag/T7GffHzZitf6TThi/images/yaml.svg?fit=max&auto=format&n=T7GffHzZitf6TThi&q=85&s=69b41e79144bc908039c2ee3abbb1c3b" theme={null}
model_name_or_path: openbmb/MiniCPM-Reranker-Light
backend: sentence_transformers # options: infinity, sentence_transformers, openai
backend_configs:
  infinity:
    bettertransformer: false
    pooling_method: auto
    device: cuda
    model_warmup: false
    trust_remote_code: true
  sentence_transformers:
    device: cuda
    trust_remote_code: true
  openai:
    model_name: text-embedding-3-small
    base_url: "https://api.openai.com/v1"
    api_key: ""

gpu_ids: 0
top_k: 5
batch_size: 16
query_instruction: ""
```

Parameter Description:

| Parameter            | Type    | Description                                                          |
| -------------------- | ------- | -------------------------------------------------------------------- |
| `model_name_or_path` | str     | Model path or name (local or HuggingFace repo)                       |
| `backend`            | str     | Select backend type: `infinity`, `sentence_transformers` or `openai` |
| `backend_configs`    | dict    | Exclusive parameter settings for each backend                        |
| `gpu_ids`            | str/int | Specify GPU ID (can be multi-card, e.g., `"0,1"`)                    |
| `top_k`              | int     | Number of reranked results returned                                  |
| `batch_size`         | int     | Sample quantity per batch                                            |
| `query_instruction`  | str     | Query prefix hint, used for prompt engineering or query modification |

`backend_configs` Detailed Description:

| Backend                    | Parameter           | Description                                                    |
| -------------------------- | ------------------- | -------------------------------------------------------------- |
| **infinity**               | `device`            | Device type (cuda / cpu)                                       |
|                            | `bettertransformer` | Whether to enable accelerated inference                        |
|                            | `pooling_method`    | Vector pooling strategy                                        |
|                            | `model_warmup`      | Whether to warmup model                                        |
|                            | `trust_remote_code` | Whether to trust remote code (Required for HuggingFace models) |
| **sentence\_transformers** | `device`            | Device type (cuda / cpu)                                       |
|                            | `trust_remote_code` | Whether to trust remote code                                   |
| **openai**                 | `model_name`        | API Model name                                                 |
|                            | `base_url`          | API access address                                             |
|                            | `api_key`           | OpenAI API Key                                                 |