mongodb taking too much time for old entries - node.js

Question

i am new in mongodb and i am facing an issue, i have around millions of documents in my collectionand i am trying to find single entry using findOne({}) command and when i am trying to find recent entries then response comes in miliseconds but when i am trying to fetch older entries around 600 millionth document then it takes around 2 minutes on mongo shell and my node server gives
{ MongoErro : connection 1 to 127.0.0.1:27017 timed out }
and my nodejs server sends an empty response. can any one tell me what should i do to resolve this issueThanks in advance
explain gives me
db.contacts.find({"phoneNumber":"9165900137"}).explain("executionStats")
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "meanApp.contacts",
"indexFilterSet" : false,
"parsedQuery" : {
"phoneNumber" : {
"$eq" : "9165900137"
}
},
"winningPlan" : {
"stage" : "COLLSCAN",
"filter" : {
"phoneNumber" : {
"$eq" : "9165900137"
}
},
"direction" : "forward"
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1,
"executionTimeMillis" : 321188,
"totalKeysExamined" : 0,
"totalDocsExamined" : 495587806,
"executionStages" : {
"stage" : "COLLSCAN",
"filter" : {
"phoneNumber" : {
"$eq" : "9165900137"
}
},
"nReturned" : 1,
"executionTimeMillisEstimate" : 295230,
"works" : 495587808,
"advanced" : 1,
"needTime" : 495587806,
"needYield" : 0,
"saveState" : 3871779,
"restoreState" : 3871779,
"isEOF" : 1,
"invalidates" : 0,
"direction" : "forward",
"docsExamined" : 495587806
}
},
"serverInfo" : {
"host" : "li1025-15.members.linode.com",
"port" : 27017,
"version" : "3.2.16",
"gitVersion" : "056bf45128114e44c5358c7a8776fb582363e094"
},
"ok" : 1
}

Answer 1

As indicated in the explain plan results, the current query is doing Collection Scan. This means it has to scan every document in collection to produce the match and you have got about half a billion documents.
Try adding this index and it might take a bit to create it.
db.contacts.createIndex( { phoneNumber: 1 }, { background: true } )
Run the query once the index creation is successful, you must see a dramatic improvement in performance. To be certain whether index got picked up, try explain again and it should no longer say COLLSCAN.