Overview of the TREC 2019 deep learning track
https://arxiv.org/abs/2003.07820
The document retrieval task has a corpus of 3.2 million documents with 367 thousand training queries
The passage retrieval task has a corpus of 8.8 million passages with 503 thousand training queries
Both tasks have large training sets based on human relevance assessments, derived from MS MARCO (3. Dataset)
https://microsoft.github.io/msmarco/TREC-Deep-Learning-2019