  k-nearest-neighbor machine translation (kNN-MT) boosts the translation
quality of a pre-trained neural machine translation (NMT) model by utilizing
translation examples during decoding. Translation examples are stored in a
vector database, called a datastore, which contains one entry for each target
token from the parallel data it is made from. Due to its size, it is
computationally expensive both to construct and to retrieve examples from the
datastore. In this paper, we present an efficient and extensible kNN-MT
framework, knn-seq, for researchers and developers that is carefully designed
to run efficiently, even with a billion-scale large datastore. knn-seq is
developed as a plug-in on fairseq and easy to switch models and kNN indexes.
Experimental results show that our implemented kNN-MT achieves a comparable
gain to the original kNN-MT, and the billion-scale datastore construction took
2.21 hours in the WMT'19 German-to-English translation task. We publish our
knn-seq as an MIT-licensed open-source project and the code is available on
https://github.com/naist-nlp/knn-seq . The demo video is available on
https://youtu.be/zTDzEOq80m0 .
