This release brings embedding quantization: a way to heavily speed up retrieval & other tasks, and a new powerful loss function: GISTEmbedLoss.
Install this version with
pip install sentence-transformers==2.6.0
Embedding Quantization
Embeddings may be challenging to scale up, which leads to expensive solutions and high latencies. However, there is a new approach to counter this problem; it entails reducing the size of each of the individual values in the embedding: Quantization. Experiments on quantization have shown that we can maintain a large amount of performance while significantly speeding up computation and saving on memory, storage, and costs.
To be specific, using binary quantization may result in retaining 96% of the retrieval performance, while speeding up retrieval by 25x and saving on memory & disk space with 32x. Do not underestimate this approach! Read more about Embedding Quantization in our extensive blogpost.
Binary and Scalar Quantization
Two forms of quantization exist at this time: binary and scalar (int8). These quantize embedding values from float32 into binary and int8, respectively. For Binary quantization, you can use the following snippet:
from sentence_transformers import SentenceTransformer
from sentence_transformers.quantization import quantize_embeddings
1. Load an embedding model
model = SentenceTransformer("mixedbread-ai/mxbai-embed-large-v1")
2a. Encode some text using "binary" quantization
binary_embeddings = model.encode(
["I am driving to the lake.", "It is a beautiful day."],
precision="binary",
)
2b. or, encode some text without quantization & apply quantization afterwards
embeddings = model.encode(["I am driving to the lake.", "It is a beautiful day."])
binary_embeddings = quantize_embeddings(embeddings, precision="binary")
GISTEmbedLoss, as introduced in Solatorio (2024), is a guided variant of the more standard in-batch negatives (MultipleNegativesRankingLoss) loss. Both loss functions are provided with a list of (anchor, positive) pairs, but while MultipleNegativesRankingLoss uses anchor_i and positive_i as positive pair and all positive_j with i != j as negative pairs, GISTEmbedLoss uses a second model to guide the in-batch negative sample selection.
This can be very useful, because it is plausible that anchor_i and positive_j are actually quite semantically similar. In this case, GISTEmbedLoss would not consider them a negative pair, while MultipleNegativesRankingLoss would. When finetuning MPNet-base on the AllNLI dataset, these are the Spearman correlation based on cosine similarity using the STS Benchmark dev set (higher is better):
The blue line is MultipleNegativesRankingLoss, whereas the grey line is GISTEmbedLoss with the small all-MiniLM-L6-v2 as the guide model. Note that all-MiniLM-L6-v2 by itself does not reach 88 Spearman correlation on this dataset, so this is really the effect of two models (mpnet-base and all-MiniLM-L6-v2) reaching a performance that they could not reach separately.
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Updates the requirements on sentence-transformers to permit the latest version.
Release notes
Sourced from sentence-transformers's releases.
... (truncated)
Commits
a5f7749
Release v2.6.013a9f3f
[feat
] Add binary & scalar embedding quantization support to Sentence Trans...e6af66f
Also update return docstring of encode_multi_process (#2548)caaa28d
Fix SentenceTransformer encode documentation return type default (numpy vecto...87f4180
[deprecation
] Deprecatesave_to_hub
in favor ofpush_to_hub
; add safe_s...fc2a2d8
Enable saving modules as pytorch_model.bin (#2542)b9255d9
Add 'get_config_dict' method to GISTEmbedLoss for better model cards (#2543)465d4f0
Add GISTEmbedLoss (#2535)66e0ee3
Fix CrossEncoder.rank default value fortop_k
(#2518)aad0642
Don't always normalize the embeddings in clustering example (#2520)Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting
@dependabot rebase
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