Inverted File Index

Also known as: IVF

The inverted file index partitions the vector space into a fixed number of clusters — computed via k-means — and assigns each vector to its nearest cluster centroid. At query time, only the vectors in the nearest few clusters are compared, sharply reducing the search scope. IVF is memory-efficient and scales well to large corpora, but it requires all vectors to be present at index build time and benefits from periodic rebuilds as data distributions shift.