MongoDB. Homework 4.

Homework: Homework 4.1

Suppose you have a collection with the following indexes:

> db.products.getIndexes()
[
 {
  "v" : 1,
  "key" : {
   "_id" : 1
  },
  "ns" : "store.products",
  "name" : "_id_"
 },
 {
  "v" : 1,
  "key" : {
   "sku" : 1
  },
                "unique" : true,
  "ns" : "store.products",
  "name" : "sku_1"
 },
 {
  "v" : 1,
  "key" : {
   "price" : -1
  },
  "ns" : "store.products",
  "name" : "price_-1"
 },
 {
  "v" : 1,
  "key" : {
   "description" : 1
  },
  "ns" : "store.products",
  "name" : "description_1"
 },
 {
  "v" : 1,
  "key" : {
   "category" : 1,
   "brand" : 1
  },
  "ns" : "store.products",
  "name" : "category_1_brand_1"
 },
 {
  "v" : 1,
  "key" : {
   "reviews.author" : 1
  },
  "ns" : "store.products",
  "name" : "reviews.author_1"
 }

Which of the following queries can utilize an index. Check all that apply.

db.products.find({'brand':"GE"}).sort({price:1})db.products.find({$and:[{price:{$gt:30}},{price:{$lt:50}}]}).sort({brand:1})

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.find({"user.followers_count":{$gt:1000}}).sort({"created_at" : 1 }).limit(10).skip(5000).explain()
{
        "cursor" : "BtreeCursor created_at_-1 reverse",
        "isMultiKey" : false,
        "n" : 10,
        "nscannedObjects" : 46462,
        "nscanned" : 46462,
        "nscannedObjectsAllPlans" : 49763,
        "nscannedAllPlans" : 49763,
        "scanAndOrder" : false,
        "indexOnly" : false,
        "nYields" : 0,
        "nChunkSkips" : 0,
        "millis" : 205,
        "indexBounds" : {
                "created_at" : [
                        [
                                {
                                        "$minElement" : 1
                                },
                                {
                                        "$maxElement" : 1
                                }
                        ]
                ]
        },
        "server" : "localhost.localdomain:27017"
}

This query performs a collection scan.The query uses an index to determine the order in which to return result documents.The query visits 46462 documents.

Homework: Homework 4.3 

Пишем 3 строки для добавления индексов: 

db.posts.ensureIndex({date:-1})

db.posts.ensureIndex({permalink:-1})

db.posts.ensureIndex({tags:-1,date:-1})

В итоге:

Tests Passed for HW 4.3. Your HW 4.3 validation code is 34f9jr29sh29f20fsplinv

Homework: Homework 4.4

In this problem you will analyze a profile log taken from a mongoDB instance. To start, please download sysprofile.json from Download Handout link and import it with the following command:

mongoimport -d m101 -c profile < sysprofile.json

Now query the profile data, looking for all queries to the students collection in the database school2, sorted in order of decreasing latency. What is the latency of the longest running operation to the collection, in milliseconds?

4715344305018158203217