# Scalable Frequency- and Length-Aware Subdocument Deduplication for Large Language Model Pretraining

arXiv: https://arxiv.org/abs/2608.03089 · HTML: https://mlsanity.com/paper/2608.03089/

## Key facts

- No citing papers in the map yet (data through 14 Oct 2026).
- Builds on 23 of its 31 references that are in the map.
- First posted on arXiv 4 Aug 2026.

## Builds on (most cited first, 23 of 23)

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- [The Pile: An 800GB Dataset of Diverse Text for Language Modeling](https://mlsanity.com/paper/2101.00027/) (2020)
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- [SoftDedup: an Efficient Data Reweighting Method for Speeding Up Language Model Pre-training](https://mlsanity.com/paper/2407.06654/) (2024)
- [Hy-MT2: A Family of Fast, Efficient and Powerful Multilingual Translation Models in the Wild](https://mlsanity.com/paper/2605.22064/) (2026)

## Abstract (arXiv)

Large-scale pretraining corpora contain substantial duplicate content. Although document-level deduplication is widely used, removing subdocument-level redundancy remains challenging. At corpus scale, suffix-array-based methods are commonly applied independently within shards, leaving cross-shard duplicates undetected and making the resulting retention behavior sensitive to the sharding configuration. Hash-based methods enable global exact duplicate counting, but often rely on fixed copy-retention policies that cannot accommodate heterogeneous repetition patterns. We propose a scalable subdocument deduplication framework that decouples duplicate detection from copy retention. It identifies duplicate groups through natural-boundary segmentation, normalized exact hashing, and distributed aggregation, and then applies an explicit frequency- and length-aware retention policy that allocates an adaptive copy budget to each group, retaining more copies of low-frequency or short repetitions while more aggressively deleting high-frequency or long ones. Experiments on FineWeb-Edu and a code-containing web corpus show that models trained on data processed by our method achieve the best overall performance among the evaluated settings. These results underscore the importance of explicit copy-retention control.