I have a collection of devices with the following set of indices:
{
"v" : 1,
"key" :
{ "sdk.id" : 1,
"sdk.createdAt" : 1,
"sdk.updatedAt" : 1,
"deviceInfo.isTablet" : 1 },
"name" : "sdk.id_1_sdk.createdAt_1_sdk.updatedAt_1_deviceInfo.isTablet_1",
"ns" : "company.Device"
}
My document looks like:
{
_id: ObjectId("something"),
property: 'abcd',
sdk: [
{ id: 'ab', createdAt: new Date(), updatedAt: new Date()},
{ id: 'ac', createdAt: new Date(), updatedAt: new Date()},
]
}
When I do db.Device.explain(1).find({'sdk.id': 'ab'}).count(), I get:
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "company.Device",
"indexFilterSet" : false,
"parsedQuery" : {
"sdk.id" : {
"$eq" : "ab"
}
},
"winningPlan" : {
"stage" : "COUNT",
"inputStage" : {
"stage" : "COUNT_SCAN",
"keyPattern" : {
"sdk.id" : 1,
"sdk.createdAt" : 1,
"sdk.updatedAt" : 1,
"deviceInfo.isTablet" : 1
},
"indexName" : "sdk.id_1_sdk.createdAt_1_sdk.updatedAt_1_deviceInfo.isTablet_1",
"isMultiKey" : true
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 0,
"executionTimeMillis" : 712,
"totalKeysExamined" : 569865,
"totalDocsExamined" : 0,
"executionStages" : {
"stage" : "COUNT",
"nReturned" : 0,
"executionTimeMillisEstimate" : 636,
"works" : 569865,
"advanced" : 0,
"needTime" : 569864,
"needFetch" : 0,
"saveState" : 4452,
"restoreState" : 4452,
"isEOF" : 1,
"invalidates" : 0,
"nCounted" : 569863,
"nSkipped" : 0,
"inputStage" : {
"stage" : "COUNT_SCAN",
"nReturned" : 569863,
"executionTimeMillisEstimate" : 616,
"works" : 569864,
"advanced" : 569863,
"needTime" : 1,
"needFetch" : 0,
"saveState" : 4452,
"restoreState" : 4452,
"isEOF" : 1,
"invalidates" : 0,
"keysExamined" : 569865,
"keyPattern" : {
"sdk.id" : 1,
"sdk.createdAt" : 1,
"sdk.updatedAt" : 1,
"deviceInfo.isTablet" : 1
},
"indexName" : "sdk.id_1_sdk.createdAt_1_sdk.updatedAt_1_deviceInfo.isTablet_1",
"isMultiKey" : true
}
},
"allPlansExecution" : [ ]
},
"serverInfo" : {
"host" : "rs-primary",
"port" : 27000,
"version" : "3.0.2",
"gitVersion" : "6201872043ecbbc0a4cc169b5482dcf385fc464f"
},
"ok" : 1
}
As you can see, the request is very slow, and it has only been added since we switched to WiredTiger (it used to be).
The collection contains ~ 600 thousand documents and ~ 550 thousand documents with sdk.id$ eq ab.
Can someone explain the explanation above to me? I can not find information about isEOF, saveState and restoreState
thank