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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