Steps : Install docker : curl -fsSL get.docker.com -o get-docker.sh sh get-docker.sh (cli 1) Start a standalone mongod v2.2 : docker run --rm --name some-mongo mongo:2.2 --smallfiles --nojournal (cli 2) Open a mongo shell to this mongod : docker exec -it some-mongo "mongo" (cli 2) Create index, data, and find explain : db.createCollection( 'testIndex' ) db.testIndex.ensureIndex({a:1,b:1,c:1}) for ( var i=1;i++<500;){db.testIndex.insert({a:i,b:4,c:i+5});} for ( var i=1;i++<500;){db.testIndex.insert({a:i,b:6,c:i+5});} db.testIndex.find({c:{$lt:100}}).sort({a:1,b:1}).explain() # do an explain( "executionStats" ) instead since v3.0 # (cli 1) Stop and remove this mongod with a [Ctrl]+[C] Start again at step 2, with each mongod version ("mongo:2.4", "mongo:2.6", "mongo:3.0", "mongo:3.2", "mongo:3.4", "mongo:3.5", etc). Optionally, clean un-used docker images to free disk space : docker rmi $(docker images -q) Results : mongod version totalKeysExamined (nscanned) totalDocsExamined (nscannedObjects) nReturned (n) 2.2.7 942 186 186 2.4.14 942 186 186 2.6.12 998 998 186 3.0.15 998 998 186 3.2.16 998 998 186 3.4.9 998 998 186 3.5.13 998 998 186 More details : In 2.2 and 2.4, "indexBounds" looks something like this : "indexBounds" : { "a" : [ [ { "$minElement" : 1 }, { "$maxElement" : 1 } ] ], "b" : [ [ { "$minElement" : 1 }, { "$maxElement" : 1 } ] ], "c" : [ [ -1.7976931348623157e+308, 100 ] ] }, But in 2.6 an above : "indexBounds" : { "a" : [ [ { "$minElement" : 1 }, { "$maxElement" : 1 } ] ], "b" : [ [ { "$minElement" : 1 }, { "$maxElement" : 1 } ] ], "c" : [ [ { "$minElement" : 1 }, { "$maxElement" : 1 } ] ] },