db.getSiblingDB( "admin" ).runCommand( { setParameter: 1, logLevel: 3 } ) db.foo.ensureIndex({a: 1}) db.foo.ensureIndex({b: 1}) db.foo.insert({a: 1, b: 3}) db.foo.insert({a: 2, b: 5}) db.foo.insert({a: 3, b: 7}) db.foo.find({a: {$gt: 2}, b: {$gt: 3}}).explain( true ) Result produced: { "cursor" : "BtreeCursor a_1", "isMultiKey" : false, "n" : 1, "nscannedObjects" : 1, "nscanned" : 1, "nscannedObjectsAllPlans" : 1, "nscannedAllPlans" : 1, "scanAndOrder" : false, "indexOnly" : false, "nYields" : 0, "nChunkSkips" : 0, "millis" : 0, "indexBounds" : { "a" : [ [ 2, Infinity ] ] }, "allPlans" : [ { "cursor" : "BtreeCursor a_1", "isMultiKey" : false, "n" : 1, "nscannedObjects" : 1, "nscanned" : 1, "scanAndOrder" : false, "indexOnly" : false, "nChunkSkips" : 0, "indexBounds" : { "a" : [ [ 2, Infinity ] ] } } ], "server" : "Jonathans-MacBook-Pro.local:27017", "filterSet" : false, "stats" : { "type" : "KEEP_MUTATIONS", "works" : 3, "yields" : 0, "unyields" : 0, "invalidates" : 0, "advanced" : 1, "needTime" : 0, "isEOF" : 1, "children" : [ { "type" : "FETCH", "works" : 2, "yields" : 0, "unyields" : 0, "invalidates" : 0, "advanced" : 1, "needTime" : 0, "isEOF" : 1, "alreadyHasObj" : 0, "forcedFetches" : 0, "matchTested" : 1, "children" : [ { "type" : "IXSCAN", "works" : 1, "yields" : 0, "unyields" : 0, "invalidates" : 0, "advanced" : 1, "needTime" : 0, "isEOF" : 1, "keyPattern" : "{ a: 1.0 }", "isMultiKey" : 0, "boundsVerbose" : "field #0['a']: (2.0, inf.0]", "yieldMovedCursor" : 0, "dupsTested" : 0, "dupsDropped" : 0, "seenInvalidated" : 0, "matchTested" : 0, "keysExamined" : 1, "children" : [ ] } ] } ] } } Observed in mongod log: 2014-07-18T10:27:58.768-0400 [conn1] Running query: query: { a: { $gt: 2.0 }, b: { $gt: 3.0 } } sort: {} projection: {} 2014-07-18T10:27:58.768-0400 [conn1] Relevant index 0 is kp: { a: 1.0 } io: { v: 1, key: { a: 1.0 }, name: "a_1", ns: "test.foo" } 2014-07-18T10:27:58.768-0400 [conn1] Relevant index 1 is kp: { b: 1.0 } io: { v: 1, key: { b: 1.0 }, name: "b_1", ns: "test.foo" } 2014-07-18T10:27:58.768-0400 [conn1] Scoring query plan: IXSCAN { a: 1.0 } planHitEOF=1 2014-07-18T10:27:58.769-0400 [conn1] score(1.5003) = baseScore(1) + productivity((1 advanced)/(2 works) = 0.5) + tieBreakers(0.0001 noFetchBonus + 0.0001 noSortBonus + 0.0001 noIxisectBonus = 0.0003) 2014-07-18T10:27:58.769-0400 [conn1] Scoring query plan: IXSCAN { b: 1.0 } planHitEOF=0 2014-07-18T10:27:58.769-0400 [conn1] score(1.5003) = baseScore(1) + productivity((1 advanced)/(2 works) = 0.5) + tieBreakers(0.0001 noFetchBonus + 0.0001 noSortBonus + 0.0001 noIxisectBonus = 0.0003) 2014-07-18T10:27:58.769-0400 [conn1] Scoring query plan: IXSCAN { a: 1.0 }, IXSCAN { b: 1.0 } planHitEOF=0 2014-07-18T10:27:58.769-0400 [conn1] score(1.0002) = baseScore(1) + productivity((0 advanced)/(2 works) = 0) + tieBreakers(0.0001 noFetchBonus + 0.0001 noSortBonus + 0 noIxisectBonus = 0.0002) 2014-07-18T10:27:58.769-0400 [conn1] Winning plan: IXSCAN { a: 1.0 } 2014-07-18T10:27:58.769-0400 [conn1] query test.foo query: { query: { a: { $gt: 2.0 }, b: { $gt: 3.0 } }, $explain: true } planSummary: IXSCAN { a: 1.0 } ntoreturn:0 ntoskip:0 nscanned:1 nscannedObjects:1 keyUpdates:0 numYields:0 locks(micros) r:789 nreturned:1 reslen:1214 0ms