MongoDB not using index when sorting - mongodb

Question

I'm using mongo 4.0.12 and I'm trying to tune my most executed query:
db.getCollection('ServiceInvoice').find(
{
"Provider.ParentId": "60f9d7631b1f243eb82903ee",
"Provider._id": "60f9d803fa27e34fdc4ec159",
"Environment": 1,
"Status": 2,
"IssuedOn":
{
"$gte": { DateTime: new Date("2022-02-01T00:00:00Z") },
"$lte": { DateTime: new Date("2022-02-01T23:59:59Z") }
}
}).limit(50).skip(1050).sort({ "IssueOn.DateTime": -1 })
using an index like:
{
"Environment" : 1.0,
"Provider.ParentId" : 1.0,
"Provider._id" : 1.0,
"Status" : 1.0,
"IssuedOn" : 1.0,
"IssuedOn.DateTime" : -1.0
}
and gives me this explain:
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "test.ServiceInvoice",
"indexFilterSet" : false,
"parsedQuery" : {
"$and" : [
{
"Environment" : {
"$eq" : 1.0
}
},
{
"Provider.ParentId" : {
"$eq" : "60f9d7631b1f243eb82903ee"
}
},
{
"Provider._id" : {
"$eq" : "60f9d803fa27e34fdc4ec159"
}
},
{
"Status" : {
"$eq" : 2.0
}
},
{
"IssuedOn" : {
"$lte" : {
"DateTime" : ISODate("2022-02-01T23:59:59.000Z")
}
}
},
{
"IssuedOn" : {
"$gte" : {
"DateTime" : ISODate("2022-02-01T00:00:00.000Z")
}
}
}
]
},
"winningPlan" : {
"stage" : "SKIP",
"skipAmount" : 0,
"inputStage" : {
"stage" : "SORT",
"sortPattern" : {
"IssueOn.DateTime" : -1.0
},
"limitAmount" : 1100,
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"Environment" : 1.0,
"Provider.ParentId" : 1.0,
"Provider._id" : 1.0,
"Status" : 1.0,
"IssuedOn" : 1.0,
"IssuedOn.DateTime" : -1.0
},
"indexName" : "Environment_1_Provider.ParentId_1_Provider._id_1_Status_1_IssueOn_1_IssueOn.DateTime_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"Environment" : [],
"Provider.ParentId" : [],
"Provider._id" : [],
"Status" : [],
"IssuedOn" : [],
"IssuedOn.DateTime" : []
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"Environment" : [
"[1.0, 1.0]"
],
"Provider.ParentId" : [
"[\"60f9d7631b1f243eb82903ee\", \"60f9d7631b1f243eb82903ee\"]"
],
"Provider._id" : [
"[\"60f9d803fa27e34fdc4ec159\", \"60f9d803fa27e34fdc4ec159\"]"
],
"Status" : [
"[2.0, 2.0]"
],
"IssuedOn" : [
"[{ DateTime: new Date(1643673600000) }, { DateTime: new Date(1643759999000) }]"
],
"IssuedOn.DateTime" : [
"[MaxKey, MinKey]"
]
}
}
}
}
}
},
"rejectedPlans" : []
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 50,
"executionTimeMillis" : 99,
"totalKeysExamined" : 31622,
"totalDocsExamined" : 31622,
"executionStages" : {
"stage" : "SKIP",
"nReturned" : 50,
"executionTimeMillisEstimate" : 6,
"works" : 32725,
"advanced" : 50,
"needTime" : 32674,
"needYield" : 0,
"saveState" : 255,
"restoreState" : 255,
"isEOF" : 1,
"invalidates" : 0,
"skipAmount" : 0,
"inputStage" : {
"stage" : "SORT",
"nReturned" : 1100,
"executionTimeMillisEstimate" : 6,
"works" : 32725,
"advanced" : 1100,
"needTime" : 31624,
"needYield" : 0,
"saveState" : 255,
"restoreState" : 255,
"isEOF" : 1,
"invalidates" : 0,
"sortPattern" : {
"IssueOn.DateTime" : -1.0
},
"memUsage" : 3057213,
"memLimit" : 33554432,
"limitAmount" : 1100,
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"nReturned" : 31622,
"executionTimeMillisEstimate" : 4,
"works" : 31624,
"advanced" : 31622,
"needTime" : 1,
"needYield" : 0,
"saveState" : 255,
"restoreState" : 255,
"isEOF" : 1,
"invalidates" : 0,
"inputStage" : {
"stage" : "FETCH",
"nReturned" : 31622,
"executionTimeMillisEstimate" : 3,
"works" : 31623,
"advanced" : 31622,
"needTime" : 0,
"needYield" : 0,
"saveState" : 255,
"restoreState" : 255,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 31622,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 31622,
"executionTimeMillisEstimate" : 1,
"works" : 31623,
"advanced" : 31622,
"needTime" : 0,
"needYield" : 0,
"saveState" : 255,
"restoreState" : 255,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"Environment" : 1.0,
"Provider.ParentId" : 1.0,
"Provider._id" : 1.0,
"Status" : 1.0,
"IssuedOn" : 1.0,
"IssuedOn.DateTime" : -1.0
},
"indexName" : "Environment_1_Provider.ParentId_1_Provider._id_1_Status_1_IssueOn_1_IssueOn.DateTime_-1",
"isMultiKey" : false,
"multiKeyPaths" : {
"Environment" : [],
"Provider.ParentId" : [],
"Provider._id" : [],
"Status" : [],
"IssuedOn" : [],
"IssuedOn.DateTime" : []
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"Environment" : [
"[1.0, 1.0]"
],
"Provider.ParentId" : [
"[\"60f9d7631b1f243eb82903ee\", \"60f9d7631b1f243eb82903ee\"]"
],
"Provider._id" : [
"[\"60f9d803fa27e34fdc4ec159\", \"60f9d803fa27e34fdc4ec159\"]"
],
"Status" : [
"[2.0, 2.0]"
],
"IssuedOn" : [
"[{ DateTime: new Date(1643673600000) }, { DateTime: new Date(1643759999000) }]"
],
"IssuedOn.DateTime" : [
"[MaxKey, MinKey]"
]
},
"keysExamined" : 31622,
"seeks" : 1,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
}
}
},
"allPlansExecution" : []
},
"serverInfo" : {
"host" : "d4ef6b3e9c6c",
"port" : 27017,
"version" : "4.0.12",
"gitVersion" : "5776e3cbf9e7afe86e6b29e22520ffb6766e95d4"
},
"ok" : 1.0
}
However, dbKoda keeps me saying that I must create an index for sorting.
I've already tried to create a separated index for IssuedOn.DateTime, but it keeps me recommending the creation and I don't see any effects.
How can I solve this problem? (Changes to the document fields are not an option).

Answer 1

According to these threads - MongoDB - Index not being used when sorting and limiting on ranged query and https://emptysqua.re/blog/optimizing-mongodb-compound-indexes/
A compund Index should be created following this order:
Equality Tests: Add all equality-tested fields to the compound index, in any order;
Sort Fields (ascending / descending only matters if there are multiple sort fields): Add sort fields to the index in the same order and direction as your query's sort;
Range Filters: First, add the range filter for the field with the lowest cardinality (fewest distinct values in the collection). Then the next lowest-cardinality range filter, and so on to the highest-cardinality.
So, the solution was creating an index like this:
{
"Environment" : 1.0,
"Provider.ParentId" : 1.0,
"Provider._id" : 1.0,
"Status" : 1.0,
"IssuedOn.DateTime" : -1.0,
"IssuedOn" : 1.0
}
And now, the query uses the index for sorting and fetch only the records in range.