Infini-gram mini: Exact n-gram Search at the Internet Scale with
  FM-Index
Authors: name: Hao Xu; name: Jiacheng Liu; name: Yejin Choi; name: Noah A. Smith; name: Hannaneh Hajishirzi
Published: 2025-06-13 21:13:57

Abstract: Language models are trained mainly on massive text data from the Internet,
and it becomes increasingly important to understand this data source.
Exact-match search engines enable searching in large text corpora -- counting
string appearances and retrieving the enclosing documents -- yet the high
storage overhead hinders their application on Internet-scale data. We present
Infini-gram mini, an efficient and scalable system that can make petabyte-level
text corpora searchable. Based on the FM-index data structure (Ferragina and
Manzini, 2000), which simultaneously indexes and compresses text, our system
creates indexes with size only 44% of the corpus. Infini-gram mini greatly
improves upon the best existing implementation of FM-index in terms of indexing
speed (18times) and memory use during both indexing (3.2times reduction)
and querying (down to a negligible amount). We index 46TB of Internet text in
50 days with a single 128-core CPU node (or 19 hours if using 75 such nodes).
We show one important use case of Infini-gram mini in a large-scale analysis of
benchmark contamination. We find several core LM evaluation benchmarks to be
heavily contaminated in Internet crawls (up to 40% in SQuAD), which could lead
to overestimating the capabilities of language models if trained on such data.
We host a benchmark contamination bulletin to share the contamination rate of
many core and community-contributed benchmarks. We also release a web interface
and an API endpoint to serve general search queries on Infini-gram mini
indexes.