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Type:
Bug
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Status: Closed
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Priority:
Major - P3
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Resolution: Duplicate
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Affects Version/s: 3.4.9
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Fix Version/s: None
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Component/s: None
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Labels:
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Operating System:ALL
This may be a clarification to be made in the documentation, but here is my bug report anyway on this subject.
Say I have a collection of products (I removed ObjectID for readability) with an index on "unique_identifier" :
Collection : products
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db.products.insert([
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{"unique_identifier":"A", "name": "My first product"}, |
{"unique_identifier":"B", "name": "My second product"}, |
{"unique_identifier":"C", "name": "My third product"} |
]);
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db.products.createIndex({"unique_identifier":1}); |
And I created a view on this collection, with a simple $project stage to rename the "unique_identifier" field to "sku" (because I need to)
db.createView("pview", "products", [{"$project":{"sku":"$unique_identifier", "name":1}}]); |
Also, for demonstration purpose, I have another view without a rename but just to remove _id field:
db.createView("pview2", "products", [{"$project":{"_id": 0}}]); |
Using explain on a simple find() operation, we can see that on pview, the index on "unique_identifier" is not used and a COLLSCAN is used, whether on pview2, it's an IXSCAN.
db.pview.find({'unique_identifier':'A'}).explain()['stages'][0]["$cursor"]["queryPlanner"]["winningPlan"]; |
{ "stage" : "COLLSCAN", "direction" : "forward" } |
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db.pview2.find({'unique_identifier':'A'}).explain()['stages'][0]["$cursor"]["queryPlanner"]["winningPlan"]; |
{
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"stage" : "FETCH", |
"inputStage" : { |
"stage" : "IXSCAN", |
"keyPattern" : { |
"unique_identifier" : 1 |
},
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"indexName" : "unique_identifier_1", |
"isMultiKey" : false, |
"multiKeyPaths" : { |
"unique_identifier" : [ ] |
},
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"isUnique" : false, |
"isSparse" : false, |
"isPartial" : false, |
"indexVersion" : 2, |
"direction" : "forward", |
"indexBounds" : { |
"unique_identifier" : [ |
"[\"A\", \"A\"]" |
]
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}
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}
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}
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Note: I found out about this using $lookup on views with renamed fields to avoid a $lookup then a $project (without the index, the $lookup takes forever, obviously)
- duplicates
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- Closed
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