Mongo DB Solution · 2 min read · Updated
Rupak NepaliPublished Nov 8, 2015
The solution to HOMEWORK 4.2 M101JS: MongoDB for Node.js Developers
Rupak NepaliPublished Nov 8, 2015
HOMEWORK: HOMEWORK 4.2
Suppose you have a collection called tweets whose documents contain information about thecreated_at time of the tweet and the user’s followers_count at the time they issued the tweet. What can you infer from the following explain output?
> db.tweets.explain("executionStats").find({"user.followers_count":{$gt:1000}}).limit(10).skip(5000).sort( { created_at : 1 } )
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "twitter.tweets",
"indexFilterSet" : false,
"parsedQuery" : {
"user.followers_count" : {
"$gt" : 1000
}
},
"winningPlan" : {
"stage" : "LIMIT",
"limitAmount" : 0,
"inputStage" : {
"stage" : "SKIP",
"skipAmount" : 0,
"inputStage" : {
"stage" : "FETCH",
"filter" : {
"user.followers_count" : {
"$gt" : 1000
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"created_at" : -1
},
"indexName" : "created_at_-1",
"isMultiKey" : false,
"direction" : "backward",
"indexBounds" : {
"created_at" : [
"[MinKey, MaxKey]"
]
}
}
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 10,
"executionTimeMillis" : 563,
"totalKeysExamined" : 251120,
"totalDocsExamined" : 251120,
"executionStages" : {
"stage" : "LIMIT",
"nReturned" : 10,
"executionTimeMillisEstimate" : 500,
"works" : 251121,
"advanced" : 10,
"needTime" : 251110,
"needFetch" : 0,
"saveState" : 1961,
"restoreState" : 1961,
"isEOF" : 1,
"invalidates" : 0,
"limitAmount" : 0,
"inputStage" : {
"stage" : "SKIP",
"nReturned" : 10,
"executionTimeMillisEstimate" : 500,
"works" : 251120,
"advanced" : 10,
"needTime" : 251110,
"needFetch" : 0,
"saveState" : 1961,
"restoreState" : 1961,
"isEOF" : 0,
"invalidates" : 0,
"skipAmount" : 0,
"inputStage" : {
"stage" : "FETCH",
"filter" : {
"user.followers_count" : {
"$gt" : 1000
}
},
"nReturned" : 5010,
"executionTimeMillisEstimate" : 490,
"works" : 251120,
"advanced" : 5010,
"needTime" : 246110,
"needFetch" : 0,
"saveState" : 1961,
"restoreState" : 1961,
"isEOF" : 0,
"invalidates" : 0,
"docsExamined" : 251120,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 251120,
"executionTimeMillisEstimate" : 100,
"works" : 251120,
"advanced" : 251120,
"needTime" : 0,
"needFetch" : 0,
"saveState" : 1961,
"restoreState" : 1961,
"isEOF" : 0,
"invalidates" : 0,
"keyPattern" : {
"created_at" : -1
},
"indexName" : "created_at_-1",
"isMultiKey" : false,
"direction" : "backward",
"indexBounds" : {
"created_at" : [
"[MinKey, MaxKey]"
]
},
"keysExamined" : 251120,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0,
"matchTested" : 0
}
}
}
}
},
"serverInfo" : {
"host" : "generic-name.local",
"port" : 27017,
"version" : "3.0.1",
"gitVersion" : "534b5a3f9d10f00cd27737fbcd951032248b5952"
},
"ok" : 1
}
Solution:
The query uses an index to determine the order in which to return result documents
The query examines 251120 documents.
Written byRupak Nepali
Author of four Opencart book.
The recent are Opencart 4 developer book and Opencart 4 user manual
