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abstract indexed · arXiv 2607.27692 · updated 2026-10-18

Recall Before You Rank: Similarity-Guided Top-$K$ Reuse for Efficient Long-Context Attention

First page of Recall Before You Rank: Similarity-Guided Top-$K$ Reuse for Efficient Long-Context Attention
From the original paper · arXiv 2607.27692Page 1. Select the image to read the PDF.

ReTopK replaces the per-token full-KV scoring and global Top-K selection step of dynamic sparse attention with a bounded per-head cache of historical query-support pairs: for each new query it retrieves similar cached queries, unions their supports with a recent window, and reranks only that compact candidate set with exact current-query scores, keeping the complete KV cache intact. The cost is extra memory for the query-support cache, the added complexity of similarity retrieval, similarity-based fallback to Exact Top-K, and periodic exact refreshes, plus the residual quality gap of approximate selection (0.50% perplexity increase at 128K, K=512). It can fail when query similarity does not predict support overlap, when the fallback triggers so often that the speedup vanishes, and because the reported gains cover only 16K-128K contexts on PG19/NIAH/LongBench and assume a Top-K attention stack already in production.

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What you would change

Check the supported GPU, tensor shapes, and precision, then replace only the relevant kernel.

Try the idea on your product

A proposed first test. Set your budget and success criteria before running it.

Check the supported GPU, tensor shapes, and precision, then replace only the relevant kernel.

Compare against

The existing kernel inside the same complete serving pipeline.

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  2. Save a small set of representative product tasks and expected outcomes. Keep evaluation tasks out of any training or tuning, and choose quality and cost limits before running.
  3. Run the baseline and the proposed change on identical inputs. Keep other settings fixed and repeat paired runs to expose variation.
  4. Save per-task outputs, failures, timings, and all usage costs. Review regressions before expanding the test.

What to measure

Numerical differences, end-to-end latency, throughput, and memory at realistic shapes.

When to keep it

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Why it was shortlisted

The technical change, research area, and reason it entered the archive.

recommendation
test
research area
attention and kernels
technical change
Query-similarity reuse of Top-K attention selections
published
2026-07-30

The method is training-free and preserves the full KV cache, making it feasible on a single 24 GB GPU serving long-context inference, but the speedup depends on the reader already using dynamic Top-K attention and on reuse reliability holding for their specific workload, so small-scale validation is required before adoption.

Central equations

Original equations, typeset for reading. Paperraft explanations connect the mechanism, its aim, and the evidence.

For each query head, ReTopK maintains a bounded FIFO cache of capacity C:

ℬt={(q¯c,S^c)}c=1|ℬt|,q¯c=qc‖qc‖2,

equation (5) · §Methodology · proposed method

where W is the window size. The resulting candidate set is

𝒜t=Unique⁡(⋃c∈ℛtS^c∪ℒt),Mt=|𝒜t|.

equation (9) · §Methodology · proposed method

For Exact Top-K, full-history QK scoring requires 𝒪⁡(Lt​d) work, followed by global Top-K selection over Lt scores. In contrast, a ReTopK reuse step requires 𝒪⁡(C​d) work for cache matching, 𝒪⁡(R​K+W) work to construct the raw candidate list, and 𝒪⁡(Mt​d) work for candidate QK scoring, followed by Top-K selection over Mt scores, where

Mt≤R​K+W≪Lt.

equation (14) · §Methodology · complexity

equations from arXiv HTML · fetched 2026-09-15

Claims and evidence

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  1. claim 01Paperraft inference
    Read the brief interpretation

    ReTopK replaces the per-token full-KV scoring and global Top-K selection step of dynamic sparse attention with a bounded per-head cache of historical query-support pairs: for each new query it retrieves similar cached queries, unions their supports with a recent window, and reranks only that compact candidate set with exact current-query scores, keeping the complete KV cache intact. The cost is extra memory for the query-support cache, the added complexity of similarity retrieval, similarity-based fallback to Exact Top-K, and periodic exact refreshes, plus the residual quality gap of approximate selection (0.50% perplexity increase at 128K, K=512). It can fail when query similarity does not predict support overlap, when the fallback triggers so often that the speedup vanishes, and because the reported gains cover only 16K-128K contexts on PG19/NIAH/LongBench and assume a Top-K attention stack already in production.

    This is a Paperraft inference. It is not pinned to a verified PDF passage.

    Inspect the source
  2. claim 02Paperraft inference

    At 128K context with K=512, 3.07x attention-computation speedup over Exact Top-K with a 0.50% perplexity increase, plus best PG19 perplexity and NIAH/LongBench scores among evaluated approximate methods.

    This is a Paperraft inference. It is not pinned to a verified PDF passage.

    Inspect the source

Exposure map

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quality

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compute and memory

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latency

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operations

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software compatibility

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security

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data and training

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reproducibility

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Continue the investigation

A reading guide for attention and kernels.

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What to inspect

Which tensor shapes, precision settings, and hardware support the reported kernel result?

Plan a fair comparison

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Questions for adoption

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Inside the paper

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