db.foo.createIndex( { subscription_id: 1, host_id: 1 }); db.foo.createIndex({ subscription_id: 1, type: 1, version_id: 1 }); let q = { "$or" : [ { "subscription_id" : "legacy-alerts" }, { "subscription_id" } ], "type" : "volume_504hour" , "volume_id" : "vol-0d4946b1a0e55a485" }; db.foo.find(q).explain(); On 7.0 the explain above produces 4 total plans. On 8.0 there is only a single plan reported and it uses the { "subscription_id": 1, "host_id" : 1 } index. Critically the latter also reports prunedSimilarIndexes" : true.