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Type:
Question
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Resolution: Done
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Priority:
Major - P3
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None
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Affects Version/s: 3.0.4
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Component/s: Index Maintenance, Querying
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None
1. Create two documents in collection "test"
{
"time": [
{
"hour": 17
},
{
"hour": 18
},
{
"day": 0
}
]
},
{
"time": [
{
"hour": 17
},
{
"hour": 19
},
{
"day": 1
}
]
}
2. Build an index:
db.test.ensureIndex({
"time.hour" : 1,
"time.day" : 1
}, {
"name" : "time.hour_1_time.day_1",
"background" : true,
})
3. Now run a query:
db.test.find({
'time.hour': 17,
'time.day': 1,
}).explain(true)
4. See that winningPlan includes a filter on 'time.day' field and index bounds do not use a value from the query
"winningPlan" : { "stage" : "FETCH", "filter" : { "time.day" : { "$eq" : NumberInt(1) } }, "inputStage" : { "stage" : "IXSCAN", "keyPattern" : { "time.hour" : NumberInt(1), "time.day" : NumberInt(1) }, "indexName" : "time.hour_1_time.day_1", "isMultiKey" : true, "direction" : "forward", "indexBounds" : { "time.hour" : [ "[17.0, 17.0]" ], "time.day" : [ "[MinKey, MaxKey]" ] } } }
The question is: why query is not fully covered by the index.