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• 动手学习RAG: 向量模型
• 动手学习RAG: BGE向量模型微调实践]()
• 动手学习RAG: BCEmbedding 向量模型 微调实践]()
• BCE ranking 微调实践]()
• GTE向量与排序模型 微调实践]()
• 模型微调中的模型序列长度]()
• 相似度与温度系数

本文我们来进行ColBERT模型的实践，按惯例，还是以open-retrievals中的代码为蓝本。在RAG兴起之后，ColBERT也获得了更多的关注。ColBERT整体结构和双塔特别相似，但迟交互式也就意味着比起一般ranking模型，交互来的更晚一些。

准备环境

pip install transformers
pip install open-retrievals

准备数据

还是采用C-MTEB/T2Reranking数据。

• 每个样本有query, positive, negative。其中query和positive构成正样本对，query和negative构成负样本对
  

使用

由于ColBERT作为迟交互式模型，既可以像向量模型一样生成向量，也可以计算相似度。BAAI/bge-m3中的colbert模型是基于XLMRoberta训练而来，因此使用ColBERT可以直接从bge-m3中加载预训练权重。

import transformers
from retrievals import ColBERT
model_name_or_path: str =  'BAAI/bge-m3' 
model = ColBERT.from_pretrained(model_name_or_path,colbert_dim=1024,    use_fp16=True,loss_fn=ColbertLoss(use_inbatch_negative=True),
)model

• 生成向量的方法

sentences_1 = ["In 1974, I won the championship in Southeast Asia in my first kickboxing match", "In 1982, I defeated the heavy hitter Ryu Long."]
sentences_2 = ['A dog is chasing car.', 'A man is playing a guitar.']output_1 = model.encode(sentences_1, normalize_embeddings=True)
print(output_1.shape, output_1)output_2 = model.encode(sentences_2, normalize_embeddings=True)
print(output_2.shape, output_2)

• 计算句子对 相似度的方法

sentences = [["In 1974, I won the championship in Southeast Asia in my first kickboxing match", "In 1982, I defeated the heavy hitter Ryu Long."],["In 1974, I won the championship in Southeast Asia in my first kickboxing match", 'A man is playing a guitar.'],
]scores_list = model.compute_score(sentences)
print(scores_list)

微调

尝试了两种方法来做，一种是调包自己写代码，一种是采用open-retrievals中的代码写shell脚本。这里我们采用第一种，另外一种方法可参考文章最后番外中的微调

import transformers
from transformers import AutoTokenizer, TrainingArguments, get_cosine_schedule_with_warmup, AdamW
from retrievals import AutoModelForRanking, RerankCollator, RerankTrainDataset, RerankTrainer, ColBERT, RetrievalTrainDataset, ColBertCollator
from retrievals.losses import ColbertLoss
transformers.logging.set_verbosity_error()model_name_or_path: str = 'BAAI/bge-m3'learning_rate: float = 1e-5
batch_size: int = 2
epochs: int = 1
output_dir: str = './checkpoints'train_dataset = RetrievalTrainDataset('C-MTEB/T2Reranking', positive_key='positive', negative_key='negative', dataset_split='dev'
)tokenizer = AutoTokenizer.from_pretrained(model_name_or_path, use_fast=False)data_collator = ColBertCollator(tokenizer,query_max_length=64,document_max_length=128,positive_key='positive',negative_key='negative',
)
model = ColBERT.from_pretrained(model_name_or_path,colbert_dim=1024,loss_fn=ColbertLoss(use_inbatch_negative=False),
)optimizer = AdamW(model.parameters(), lr=learning_rate)
num_train_steps = int(len(train_dataset) / batch_size * epochs)
scheduler = get_cosine_schedule_with_warmup(optimizer, num_warmup_steps=0.05 * num_train_steps, num_training_steps=num_train_steps)training_args = TrainingArguments(learning_rate=learning_rate,per_device_train_batch_size=batch_size,num_train_epochs=epochs,output_dir = './checkpoints',remove_unused_columns=False,gradient_accumulation_steps=8,logging_steps=100,)
trainer = RerankTrainer(model=model,args=training_args,train_dataset=train_dataset,data_collator=data_collator,
)
trainer.optimizer = optimizer
trainer.scheduler = scheduler
trainer.train()model.save_pretrained(output_dir)

训练过程中会加载BAAI/bge-m3模型权重

损失函数下降

{'loss': 7.4858, 'grad_norm': 30.484981536865234, 'learning_rate': 4.076305220883534e-06, 'epoch': 0.6024096385542169}
{'loss': 1.18, 'grad_norm': 28.68316650390625, 'learning_rate': 3.072289156626506e-06, 'epoch': 1.2048192771084336}
{'loss': 1.1399, 'grad_norm': 14.203865051269531, 'learning_rate': 2.068273092369478e-06, 'epoch': 1.8072289156626506}
{'loss': 1.1261, 'grad_norm': 24.30337905883789, 'learning_rate': 1.0642570281124499e-06, 'epoch': 2.4096385542168672}
{'train_runtime': 471.8191, 'train_samples_per_second': 33.827, 'train_steps_per_second': 1.055, 'train_loss': 2.4146631079984, 'epoch': 3.0}

评测

在C-MTEB中进行评测。微调前保留10%的数据集作为测试集验证

from datasets import load_datasetdataset = load_dataset("C-MTEB/T2Reranking", split="dev")
ds = dataset.train_test_split(test_size=0.1, seed=42)ds_train = ds["train"].filter(lambda x: len(x["positive"]) > 0 and len(x["negative"]) > 0
)ds_train.to_json("t2_ranking.jsonl", force_ascii=False)

微调前的指标：

微调后的指标：

{"dataset_revision": null,"mteb_dataset_name": "CustomReranking","mteb_version": "1.1.1","test": {"evaluation_time": 221.45,"map": 0.6950128151840831,"mrr": 0.8193114944390455}
}

番外：从语言模型直接训练ColBERT

之前的例子里是从BAAI/bge-m3继续微调，这里再跑一个从hfl/chinese-roberta-wwm-ext训练一个ColBERT模型

• 注意，从头跑需要设置更大的学习率与更多的epochs

MODEL_NAME='hfl/chinese-roberta-wwm-ext'
TRAIN_DATA="/root/kaggle101/src/open-retrievals/t2/t2_ranking.jsonl"
OUTPUT_DIR="/root/kaggle101/src/open-retrievals/t2/ft_out"cd /root/open-retrievals/srctorchrun --nproc_per_node 1 \--module retrievals.pipelines.rerank \--output_dir $OUTPUT_DIR \--overwrite_output_dir \--model_name_or_path $MODEL_NAME \--tokenizer_name $MODEL_NAME \--model_type colbert \--do_train \--data_name_or_path $TRAIN_DATA \--positive_key positive \--negative_key negative \--learning_rate 5e-5 \--bf16 \--num_train_epochs 5 \--per_device_train_batch_size 32 \--dataloader_drop_last True \--query_max_length 128 \--max_length 256 \--train_group_size 4 \--unfold_each_positive false \--save_total_limit 1 \--logging_steps 100 \--use_inbatch_negative False

微调后指标

{"dataset_revision": null,"mteb_dataset_name": "CustomReranking","mteb_version": "1.1.1","test": {"evaluation_time": 75.38,"map": 0.6865308507184888,"mrr": 0.8039965986394558}
}