db.cities
  .find( { country_code: 'GB', population: { $gte: 500000 } } )
  .*explain("executionStats)*;

{
    "queryPlanner" : {
        "plannerVersion" : 1,
        "namespace" : "demo.cities",
        "indexFilterSet" : false,
        "parsedQuery" : {
            "$and" : [
                {
                    "country_code" : {
                        "$eq" : "GB"
                    }
                },
                {
                    "population" : {
                        "$gte" : 500000
                    }
                }
            ]
        },
        "winningPlan" : {
            "stage" : "FETCH",
            "inputStage" : {
                "stage" : "IXSCAN",
                "keyPattern" : {
                    "country_code" : 1,
                    "population" : 1
                },
                "indexName" : "country_code_1_population_1",
                "isMultiKey" : false,
                "isUnique" : false,
                "isSparse" : false,
                "isPartial" : false,
                "indexVersion" : 1,
                "direction" : "forward",
                "indexBounds" : {
                    "country_code" : [
                        "[\"GB\", \"GB\"]"
                    ],
                    "population" : [
                        "[500000.0, inf.0]"
                    ]
                }
            }
        },
        "rejectedPlans" : [
            {
                "stage" : "FETCH",
                "filter" : {
                    "country_code" : {
                        "$eq" : "GB"
                    }
                },
                "inputStage" : {
                    "stage" : "IXSCAN",
                    "keyPattern" : {
                        "population" : 1,
                        "elevation" : 1
                    },
                    "indexName" : "population_1_elevation_1",
                    "isMultiKey" : false,
                    "isUnique" : false,
                    "isSparse" : false,
                    "isPartial" : false,
                    "indexVersion" : 1,
                    "direction" : "forward",
                    "indexBounds" : {
                        "population" : [
                            "[500000.0, inf.0]"
                        ],
                        "elevation" : [
                            "[MinKey, MaxKey]"
                        ]
                    }
                }
            },
            {
                "stage" : "FETCH",
                "filter" : {
                    "country_code" : {
                        "$eq" : "GB"
                    }
                },
                "inputStage" : {
                    "stage" : "IXSCAN",
                    "keyPattern" : {
                        "population" : 1,
                        "dem" : 1
                    },
                    "indexName" : "population_1_dem_1",
                    "isMultiKey" : false,
                    "isUnique" : false,
                    "isSparse" : false,
                    "isPartial" : false,
                    "indexVersion" : 1,
                    "direction" : "forward",
                    "indexBounds" : {
                        "population" : [
                            "[500000.0, inf.0]"
                        ],
                        "dem" : [
                            "[MinKey, MaxKey]"
                        ]
                    }
                }
            },
            {
                "stage" : "FETCH",
                "filter" : {
                    "population" : {
                        "$gte" : 500000
                    }
                },
                "inputStage" : {
                    "stage" : "IXSCAN",
                    "keyPattern" : {
                        "country_code" : 1,
                        "timezone" : 1,
                        "asciiname" : 1
                    },
                    "indexName" : "country_code_1_timezone_1_asciiname_1",
                    "isMultiKey" : false,
                    "isUnique" : false,
                    "isSparse" : false,
                    "isPartial" : false,
                    "indexVersion" : 1,
                    "direction" : "forward",
                    "indexBounds" : {
                        "country_code" : [
                            "[\"GB\", \"GB\"]"
                        ],
                        "timezone" : [
                            "[MinKey, MaxKey]"
                        ],
                        "asciiname" : [
                            "[MinKey, MaxKey]"
                        ]
                    }
                }
            }
        ]
    },
    "executionStats" : {
        "executionSuccess" : true,
        "nReturned" : 4,
        "executionTimeMillis" : 12,
        "totalKeysExamined" : 4,
        "totalDocsExamined" : 4,
        "executionStages" : {
            "stage" : "FETCH",
            "nReturned" : 4,
            "executionTimeMillisEstimate" : 10,
            "works" : 7,
            "advanced" : 4,
            "needTime" : 0,
            "needYield" : 1,
            "saveState" : 6,
            "restoreState" : 6,
            "isEOF" : 1,
            "invalidates" : 0,
            "docsExamined" : 4,
            "alreadyHasObj" : 0,
            "inputStage" : {
                "stage" : "IXSCAN",
                "nReturned" : 4,
                "executionTimeMillisEstimate" : 10,
                "works" : 5,
                "advanced" : 4,
                "needTime" : 0,
                "needYield" : 0,
                "saveState" : 6,
                "restoreState" : 6,
                "isEOF" : 1,
                "invalidates" : 0,
                "keyPattern" : {
                    "country_code" : 1,
                    "population" : 1
                },
                "indexName" : "country_code_1_population_1",
                "isMultiKey" : false,
                "isUnique" : false,
                "isSparse" : false,
                "isPartial" : false,
                "indexVersion" : 1,
                "direction" : "forward",
                "indexBounds" : {
                    "country_code" : [
                        "[\"GB\", \"GB\"]"
                    ],
                    "population" : [
                        "[500000.0, inf.0]"
                    ]
                },
                "keysExamined" : 4,
                "seeks" : 1,
                "dupsTested" : 0,
                "dupsDropped" : 0,
                "seenInvalidated" : 0
            }
        }
    },
    "serverInfo" : {
        "host" : "whisky",
        "port" : 27017,
        "version" : "3.3.8",
        "gitVersion" : "00ed8f3b275971093ddd2ee7d3ab558904e28af0"
    },
    "ok" : 1
}

{ "name" : "Glasgow", "country_code" : "GB", "population" : 610268 }
{ "name" : "Birmingham", "country_code" : "GB", "population" : 984333 }
{ "name" : "City of London", "country_code" : "GB", "population" : 7556900 }
{ "name" : "London", "country_code" : "GB", "population" : 7556900 }