Semi-off topic, what are some of the good algorithms to search faces with a similarity factor? Let's say I have a database of millions of faces and I want to g

Semi-off topic, what are some of the good algorithms to search faces with a similarity factor? Let's say I have a database of millions of faces and I want to go through the streaming of a video to identify all the faces showing up in the video with a 90% similarity factor. I assume the faces on each frame of the video are extracted to be queried against the face database. Would all the faces in the db loaded into memory and constructed in some data structure for efficient query? Or some mapping to SQL's standard B+ tree index with range searching can be done?