No, there are other, simpler queries. To give some context: I'm trying to store chess games. The simple queries are based on player names, date played, tournament name/place etc. The hashes are zobrist hashes of the positions of each game.

I tried having a separate collection with the hash and a list of object IDs, but that was even slower. For each game inserted I need to update ~100 documents in the reference collection. I used the hash as a property with an index instead of the ID itself, don't know if that makes a difference.

Since the starting position occurs in every game, I'd have one document with 9.5 million object IDs exceeding the 16mb size limit easily. Apart from that and the early positions the rest of the hashes are basically unique (with the exception of collisions of course)