Q-Filters: Leveraging QK Geometry for Efficient KV Cache Compression
Authors: name: Nathan Godey, name: Alessio Devoto, name: Yu Zhao, name: Simone Scardapane, name: Pasquale Minervini, name: Éric de la Clergerie, name: Benoît Sagot

Autoregressive language models rely on a Key-Value (KV) Cache, which avoids
re-computing past hidden states during generation, making it faster. As model
sizes and context lengths grow, the KV Cache becomes a significant memory
bottleneck, which calls for compression methods that limit its size during
generation. In this paper, we discover surprising properties of Query (Q) and
Key (K) vectors that allow us to efficiently approximate attention scores
without computing the attention maps. We propose Q-Filters, a training-free KV
Cache compression method that filters out less crucial Key-Value pairs based on
a single context-agnostic projection. Contrarily to many alternatives,
Q-Filters is compatible with FlashAttention, as it does not require direct
access to attention weights. Experimental results in long-context settings
demonstrate that Q-Filters is competitive with attention-based compression
methods such as SnapKV in retrieval tasks while consistently outperforming
efficient compression schemes such as Streaming-LLM in generation setups.
Notably, Q-Filters achieves a 99% accuracy in the needle-in-a-haystack task
with a x32 compression level while reducing the generation perplexity drop by
up to 65% in text generation compared to Streaming-LLM.