MCQs > IT & Programming > MongoDB MCQs > Basic MongoDB MCQs

Basic MongoDB MCQ

1. All tag values in tag sets must be _.

Answer

Correct Answer: Strings

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2. When using aggregation $convert. which is not a parameter?

Answer

Correct Answer: Output

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3. You need to add an index to the large name collection in your production database. You do not want to have disruption of service for your users and you can't afford to have a team to do the work during after hours. What should you do?

Answer

Correct Answer: Use the createIndex() command with the option background = true.

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4. What should the priority of a member be in order to prevent it from becoming the primary in replica set?

Answer

Correct Answer: Null

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5. Documents in mongodb are atomic at the ___ level

Answer

Correct Answer: Document

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6. Which projection shows only the FirstName and lastName fields of a document in the customers collection?

Answer

Correct Answer: Db.customers.find({}, {_id:0, firstName: 1, lastName: 1})

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7. What is the internal data structure of a MongoDB document?

Answer

Correct Answer: JSON (JavaScript Object Notation)

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8. How do you create a new MongoDB user?

Answer

Correct Answer: Db.createUser({})

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9. How does a --jsonArray file need to be structured?

Answer

Correct Answer: As a properly formatted JSON array

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10. After installing MongoDB on your machine, what must you do before launching Mongo?

Answer

Correct Answer: Establish security credentials.

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11. Which field is always included in a projection unless specifically excluded?

Answer

Correct Answer: _id

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12. You need to be able to quickly find a word in a text field. What should you do?

Answer

Correct Answer: Do a $text query.

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13. You have a collection with millions of documents. Each time you attempt to sort. MongoDB runs out of memory. What might help?

Answer

Correct Answer: Create an index on the field you are sorting.

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14. Suppose you are using the mongoimport command to import personnel data and there is a unique index on the email field. What happens when there are duplicate emails in the import?

Answer

Correct Answer: The import command prompts you to correct the bad record.

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15. Which MongoDB shell query will sort the customer's collection by name descending?

Answer

Correct Answer: Db.customers.find({}).sort({name: -1})

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16. From the MongoDB shell, how do you execute a JavaScript file named list.js?

Answer

Correct Answer: Load('list.js)

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17. MongoDB ships with a variety of files. Which file runs the MongoDB shell?

Answer

Correct Answer: Mongo

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18. What happens to a Replica set oplog if it runs out of memory?

Answer

Correct Answer: The oplog will be saved on one of the secondary servers.

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19. How can you improve the appearance of the output JSON that contains the _id?

Answer

Correct Answer: Use db.collection.format(numeric)

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20. What option can be passed to start the MongoDB shell without connecting to a database?

Answer

Correct Answer: -nodb

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21. To remove a database and all of its records from MongoDB, what operator should you use?

Answer

Correct Answer: DropDatabase()

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22. In MongoDB, what does a projection do?

Answer

Correct Answer: Allows you to select which fields should be in the return data

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23. What is the most accurate statement regarding MongoDB and ad hoc queries?

Answer

Correct Answer: MongoDB does not allow ad hoc queries; all queries require an index.
MongoDB allows ad hoc queries.

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24. You have just secured your previously unsecured MongoDB server, but the server is still not requiring authentication. What is the best option?

Answer

Correct Answer: Restart the mongod process.

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25. Which file in the MongoDB directly holds the MongoDB daemon?

Answer

Correct Answer: Mongo-daemon
Mongod

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26. What is the correct query to find all of the people who have a home phone number defined?

Answer

Correct Answer: Db.person.find({homePhone: {$exists: true}});

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27. When no parameters are passed to explain(), what mode does it run in?

Answer

Correct Answer: QueryPlanner mode

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28. To cleanly shut down MongoDB, what command should you use from the MongoDB shell?

Answer

Correct Answer: Db.shutdownServer()

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29. You are going to do a series of updates to multiple records. You find setting the multi option of the update() command too tiresome. What should you do instead?

Answer

Correct Answer: Use the updateMany() command instead

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30. You need to get the names of all the indexes on your current collection. What is the best way to accomplish this?

Answer

Correct Answer: Db.people.getIndexes();

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31. By default, applications direct their read operations to which member of the replica set?

Answer

Correct Answer: Primary

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32. Using the MongoDB shell, how do you remove the customer collection and its indexes?

Answer

Correct Answer: Db.customers.drop();

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33. Which MongoDB shell command deletes a single document?

Answer

Correct Answer: Db.customers.remove({_id: 1});

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34. What is NOT a standard role in MongoDB?

Answer

Correct Answer: Dbadmin

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35. You'd like a set of documents to be returned in last name, ascending order. Which query will accomplish this?

Answer

Correct Answer: Db.persons.find().sort({lastName: 1}}

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36. A MongoDB instance has at least what three files?

Answer

Correct Answer: Data, namespace, and journal

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37. Which field is required of all MongoDB documents?

Answer

Correct Answer: _id

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38. From the MongoDB shell, how do you create a new document in the customers collection?

Answer

Correct Answer: Db.customers.save({name:

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39. You want to modify an existing index. What is the best way to do this?

Answer

Correct Answer: Delete the original index and create a new index.

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40. You have a collection of thousands of students. You'd like to return the second set of 20 documents from the sorted collection. What is the proper order in which to apply the operations?

Answer

Correct Answer: Sort, skip, limit

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41. On a newly created collection, which field will have an index?

Answer

Correct Answer: The _id field

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42. . In an MongoDB mapReduce command, the reduce function should _.

Answer

Correct Answer: Not access the data

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43. To import a CSV file into MongoDB, which command should you issue?

Answer

Correct Answer: Mongoimport

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44. You have two text fields in your document and you'd like both to be quickly searchable. What should you do?

Answer

Correct Answer: Create a text index on each field.

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45. Which programming language is used to write MongoDB queries? (Alternative: In the MongoDB shell, what programming language is used to make queries?)

Answer

Correct Answer: JavaScript

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46. What is the preferred format to store geospatial data in MongoDB?

Answer

Correct Answer: GeoJSON

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47. What is true about indexes?

Answer

Correct Answer: They speed up read access while slowing down writes.

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48. Given a cursor named myCursor, pointing to the customers collection, how to you get basic info about it?

Answer

Correct Answer: MyCursor.explain()

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49. How often do the members of a replica set send heartbeats to each other?

Answer

Correct Answer: Every 2 seconds

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50. Why are ad-hoc queries useful?

Answer

Correct Answer: They run faster than indexed queries.

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51. A compound index allows you to _ ?

Answer

Correct Answer: Combine fields in different collations.

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52. One of the documents in your collection has an _id based upon an older database design and you want to change it. You write an update command to find the document and replace the _id but the _id isn't changed. How should you fix the issue?

Answer

Correct Answer: You can't. Once set, the _id field cannot be changed.

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53. Assuming you have customers collection with a firstName and lastName field, which is the correct MongoDB shell command to create an index on lastName, then firstName both ascending?

Answer

Correct Answer: Db.customers.createIndex({lastName:1, firstName: 1})

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54. How do you create a text index?

Answer

Correct Answer: Db.customers.createIndex({firstName:

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55. Which query bypasses the first 5 customers and returns the next 10?

Answer

Correct Answer: Db.customers.find({}).skip(5).limit(10)

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56. To restrict the number of records coming back from a query, which command should you use?

Answer

Correct Answer: Limit

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57. What is the purpose of an arbiter in a replica set?

Answer

Correct Answer: It casts the tie-breaking vote in an election.

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58. What is the correct option to set up Kerberos when starting MongoDBd?

Answer

Correct Answer: --setParameter authenticationMechanisms=GSSAPI

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59. What the primary database in a replica set fails, when does failover begin?

Answer

Correct Answer: Immediately

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60. What is the recommended way to delete a user?

Answer

Correct Answer: Db.dropUser(

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61. Suppose your aggregation pipeline terminated with an exception referring to exceeded memory limit. What is the best way to resolve the issue?

Answer

Correct Answer: Set allowDiskUse to true.

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62. In the MongoDB shell, how can you tell if an index was used with a query?

Answer

Correct Answer: Db.customers.find({lastName: 'smith'}).explain()

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63. Choose the shell command that connects to a MongoDB database.

Answer

Correct Answer: Mongo

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64. To import a JSON array into Mongo, what flags are needed with MongoDBimport?

Answer

Correct Answer: --jsonArray

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65. Which command returns a specific document in the user's collection?

Answer

Correct Answer: Db.users.find({_id: 1})

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66. Given an ObjectId in _id, how do you get the time it was created?

Answer

Correct Answer: _id.getTimestamp()

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67. What does a MongoDB collection consist of?

Answer

Correct Answer: Documents

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68. Which shell query displays all citizens with an age greater than or equal to 21?

Answer

Correct Answer: Db.citizens.find({age: {$gte: 21}})

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69. Which MongoDB shell command should you use to back up a database?

Answer

Correct Answer: Mongodump

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70. When should you avoid embedding one document within another in MongoDB?

Answer

Correct Answer: When there are so many embedded document updates that it becomes a bottleneck for performance

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71.

When is sharding needed? (choose all that apply)

Answer

Correct Answer: Local disk is not big enough
Vertical scaling is too expensive
Memory can't be large enough when the active dataset is big

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72.

How many chunks can there be if the shard key cardinality is 4?

Answer

Correct Answer: 4

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73.

If the value of totalKeysExamined is 30000 and the value of totalDocsExamined is 0, which option is correct?

Answer

Correct Answer: The query used an index to fetch the results

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74.

Which of the following cursor methods is used to select a particular index?

Answer

Correct Answer: hint

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75.

If you created a compound index on (X, Y, Z), which access pattern will not be able to utilize the index?

Answer

Correct Answer: Y, Z

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76.

Which of the following could be a use case where MongoDB is a good fit?

Answer

Correct Answer: When you need to store data with nested arrays

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77.

All the replica set members contain a copy of the oplog in the _____ collection.

Answer

Correct Answer: local.oplog.rs

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78.

Which statement best describes $allElementsTrue?

Answer

Correct Answer: Evaluates an array as a set and returns true if no element in the array is false. If a the array contains a nested array it does not descend into the nested array but evaluates the array at top-level

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79.

The following statement is most suitable for the following aggregation stage: "Used to select fields from the collection while aggregation".

Answer

Correct Answer: $project

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80.

Which of the following is not an aggregation operation? (choose all that apply)

Answer

Correct Answer: Update
Insert

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81.

How can you create index on a particular key in MongoDB?

Answer

Correct Answer: db.COLLECTION_NAME.createIndex({ KEY: 1 })

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82.

Which statement is valid?

Answer

Correct Answer: MongoDB shards data at the collection level.

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83.

Which of the following commands will return all the posts with a number of likes greater than 100 and less than 200, including the limit values ?

Answer

Correct Answer: db.posts.find({ likes : { $gte : 100 , $lte : 200 } } );

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84.

Which of following helps analyze a query?

Answer

Correct Answer: explain

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85.

Which of the following calls will set a 1 second limit for processing operations?

Answer

Correct Answer: .maxTimeMS(1000)

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86.

MongoDB is a process collection of documents using (...) operations

Answer

Correct Answer: Map-reduce

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87.

The code below is used to try to delete a collection in the mongo shell: db.my-collection.drop() Choose the best statement that best describes why the code fails to delete the collection.

Answer

Correct Answer: The shell's interpreter tries to apply this as subtraction

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88.

Which statement best describes the query below? db.col1.findAndModify({ query: {"name": "val1"}, update: { $inc: { "subObj.field1": 1 } });

Answer

Correct Answer: Returns a single document where name is val1 and field1 is unmodified in the returned document

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89.

Regarding Pipeline Operators in MongoDB, which of the following is an incorrect statement? (choose all that apply)

Answer

Correct Answer: $avg is an accumulator operator available only in the $group stage
$sum accumulator can be used to compute the total amount and count for each group of documents
All of the mentioned

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90.

Which option is the most suitable advantage of using embedded documents?

Answer

Correct Answer: It allows reading connected data in a single request to the database.

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91.

Which of the following methods allows to insert documents into a collection?

Answer

Correct Answer: insert

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92.

Your rs.add("....") is missing the quotation marks

Answer

Correct Answer: Hashed
Key

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93.

Which of the following is true about replica set? (choose all that apply)

Answer

Correct Answer: It's a group of servers with one primary.
It's a group of servers with many secondaries.

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94.

Which of the following is the correct call to setup replica set?

Answer

Correct Answer: None of these

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95.

What can be done to optimize aggregation pipeline?

Answer

Correct Answer: Place the $match as early in the aggregation pipeline as possible

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96.

Which of the read preference modes in a replica set configuration specify the operations to be read from the node whose network latency falls within the acceptable latency window?

Answer

Correct Answer: nearest

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97.

You are setting up replication for a mongodb cluster and you get the following error "no replset config has been received". Choose the most probable reason:

Answer

Correct Answer: You have not run rs.initiate() in the master node and rs.slaveOk() on the secondaries

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98.

You have a 10G primary partition with your data in in ' /var/lib/mongodb/'. Choose the best option to transfer data to a larger partition:

Answer

Correct Answer: Just move your folder, add symlink, then tune permissions

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99.

Which of the following calls will remove all users who are older than 21 from Users collection?

Answer

Correct Answer: db.users.remove({age: {$gt: 21}});
db.users.deleteMany({age: {$gt: 21}});

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100.

Which of the following parameters affect ObjectId?

Answer

Correct Answer: Timestamp

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101.

Which of the following is the correct calling of creating an index?

Answer

Correct Answer: db.somecollection.createIndex({key:1});
db.somecollection.ensureIndex({key:1}, { expireAfterSeconds: 3600 });

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102.

Which of the following options exists in ensureIndex method?

Answer

Correct Answer: background
unique
name

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103.

Which of the following are stages of aggregation?

Answer

Correct Answer: $sort
$skip
$limit

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104.

Which of the following is true? Check all that apply.

Answer

Correct Answer: A replica set is a group of mongodb instances that host the same data set.

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105.

Choose the best description of the query below:- db.users.find ({ "name" : /m/i } ).pretty()

Answer

Correct Answer: case insensitive query for those users whose name has 'm'

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106.

Under what conditions is it required to use the db.getCollection() method in the mongo shell to delete a collection?

Answer

Correct Answer: If your collection name includes the underscore character

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107.

For a large data set in terms of size on the volume your MongoDB is exhibiting poor write performance. Choose the most probable reason

Answer

Correct Answer: The 'index space' is to large

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108.

In a shared replica set environment, w defined the level and kind of write concern. Which of the following values of w specifies ti return success only after a majority of voting members have acknowledge?

Answer

Correct Answer: majority

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109.

Choose the statement that best describes the query below: db.myCol.find().sort({$natural:-1}).limit(50);

Answer

Correct Answer: Returns the last 50 entries in descending order

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110.

Why use replication?

Answer

Correct Answer: All of the above

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111.

For the mongo shell function below function last(N) { return db.collection.find().skip(db.collection.count() - N); }

Answer

Correct Answer: db.collection.find().skip(db.collection.count() - N)

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112.

Which of the following is the correct order in pipelining in mongo aggregation?

Answer

Correct Answer: $match, $group, $project, $sort, $skip, $limit, $unwind

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113.

How many members a replica set can have?

Answer

Correct Answer: Up to 50

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114.

Which of the following methods will shut down replica set?

Answer

Correct Answer: newReplica.stopSet();

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115.

Choose the statement that best describes how indexing improve query response time

Answer

Correct Answer: The index size is less than the collection size so the look up is quicker its that simple

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116.

For the query below db.collection.find( { x: 5 } ).sort( { z: 1} ) Choose the best index to support the query

Answer

Correct Answer: { x: 1, z: 1 }

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117.

Choose the type of query where indexes can result in slower query response time.

Answer

Correct Answer: where a query is going to return almost an entire collection

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118.

Given the below statement, please choose the most probable reason:- "You have a web application with mongodb as a backend. A query returns a resultset, however when called a second time the result set is empty."

Answer

Correct Answer: Someone just dropped the collection

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119.

Which of the following are correct index types?

Answer

Correct Answer: All of the above.

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120.

What is the minimum nodes required for replica?

Answer

Correct Answer: 2

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121.

Describe the best use case for choosing MongoDB map-reduce.

Answer

Correct Answer: For aggregation queries on small data sets

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122.

Suppose we have a collection of users with different ages. Which of the following calls will find the oldest person with the name John?

Answer

Correct Answer: db.users.aggregate({$match: {name: "John"}}, {$sort: {age: -1}}, {$limit: 1});

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123.

Choose the statement that best describes the query below: db.myCol.find().sort({_id:1});

Answer

Correct Answer: Will sort in ascending numerical order

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124.

Which of the following is a valid MongoDB document?

Answer

Correct Answer: {}

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125.

Point out the correct statement.

Answer

Correct Answer: All of the mentioned

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126.

When should one should avoid embedding one document within another in MongoDB?

Answer

Correct Answer: When writing to the complex documents is very heavy.

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127.

If the address data is frequently retrieved with the name information,how will you modify the following schema representing one to one relationship with referencing ? { _id: "joe", name: "Joe Bookreader" } { patron_id: "joe", street: "123 Fake Street", city: "Faketon", state: "MA", zip: "12345" }

Answer

Correct Answer: { _id: "joe", name: "Joe Bookreader", address: { street: "123 Fake Street", city: "Faketon", state: "MA", zip: "12345" } }

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128.

Which of following points describes when using embedded data models?

Answer

Correct Answer: To have better performance.

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129.

Which of the following fields DBRefs has?

Answer

Correct Answer: All of the above

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130.

For a mongo mapreduce flow, the emit function has the form emit(this.cId, {q1:this.Q1, q2s:this.Q2}); Choose the correct return value for the reduce function

Answer

Correct Answer: return {a:this.Q1, b:this.Q2};

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131.

For a collection that represents type A { “field1” : “val1”, “field2” : “val2” } Choose the best way to optimize the collection for updates if field2 is an Enumeration.

Answer

Correct Answer: { “field1” : “val1”, field2 : [“val2”] }

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132.

Which of the following are captured by the Database Profiler in MongoDB ?

Answer

Correct Answer: All of the above

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133.

Which of the following is a correct command to insert a document in a database called album and collection called songs?

Answer

Correct Answer: db.songs.insert( { title: "Roar", artist: "Katy Perry" } )

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134.

The query below returns a collection of users with a projection db.users.find({}, {name: 1, _id : 1}) Choose the best statement that describes how to extract a collection of users with the projection that shows the creation date

Answer

Correct Answer: Map the projection with ObjectId.getTimestamp()

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135.

Which of the following operation adds a new document to the users collection ?

Answer

Correct Answer: insert

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136.

If you are using { upsert: true } option in your update command, which of the following parameters will be used to determine if any new documents were inserted:

Answer

Correct Answer: nUpserted

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137.

Consider the following document from the products collection: { _id: 1, product_code: "1234", variations: [ { size: "L", price: 1000 }, { size: "M", price: 800 } ] } What does the following query using $elemMatch return? db.products.find( { product_code: "1234" }, { variations: { $elemMatch: { size: "L" } } } )

Answer

Correct Answer: Returns the document but with only one element in the variations array (corresponding to size L)

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138.

Which method in MongoDB replaces the existing document with the new document passed as parameter?

Answer

Correct Answer: save()

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139.

Which command can be used to check the size of a collection named user?

Answer

Correct Answer: db.user.stats()

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140.

Which of the following command can be used to check the size of a collection named user?

Answer

Correct Answer: db.user.stats()

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141.

Which of the following SQL terminilogy is same as $match in MongoDB?

Answer

Correct Answer: Both WHERE and HAVING

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142.

Choose the best description of why MongoDB performs well on a non heterogeneous cluster:

Answer

Correct Answer: Every shard in MongoDB is its own mongod

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143.

___ filters the document stream to allow only matching documents to pass unmodified into the next pipeline stage.

Answer

Correct Answer: $match

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144.

Which of the following operators is related to geography of data ?

Answer

Correct Answer: $geoNear

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145.

Sometimes the failover process may require a ____ during operation.

Answer

Correct Answer: rollback

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146.

Consider the following posts collection in MongoDB, { "_id" : 1, "post_title" : "this is post title", "tags": [ "social", "friends", "books"], // rest of the document } What will be the output of following query: db.posts.aggregate( [ { $unwind : "$tags" } ] )

Answer

Correct Answer: Return three separate documents for three separate tags

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147.

Which of the following best describes the concept of Aggregations in MongoDB ?

Answer

Correct Answer: It's the operation that process data records and return computed results, by grouping values from multiple documents together, so that it can perform a variety of operations on the grouped data to return a single result.

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148.

Which aggregation option is used to specify the fields that need to be passed to the next stage of the aggregation pipeline?

Answer

Correct Answer: $project

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149.

Which of the following best describes the concept of Replication in MongoDB ?

Answer

Correct Answer: It's the process of synchronizing data across multiple servers, providing redundancy and increases data availability, with multiple copies of data on different database servers.

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150.

Regarding indexing and performance in MongoDB, choose the correct statement :

Answer

Correct Answer: If you sometimes query on only one key and at other times query on that key combined with a second key, then creating a compound index is more efficient than creating a single-key index

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151.

In MongoDB, a query ____ consists of a combination of query, sort, and projection specifications.

Answer

Correct Answer: shape

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152.

What is a covered query?

Answer

Correct Answer: Query in which fields used in the query are part of an index used in the query and the fields returned in the results are in the same index.

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153.

Regarding aggregation pipeline optimization concepts in MongoDB, if you have a $sort followed by a $match:

Answer

Correct Answer: $match moves before $sort to minimize the number of objects to sort

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154.

Regarding storage in MongoDB, which of the following is incorrect?

Answer

Correct Answer: When running a 32-bit build of MongoDB, the total storage size for the server, including data and indexes, is 2 gigabytes. For this reason, do not deploy MongoDB to production on 32-bit machines.
When journaling is enabled, MongoDB stores and applies write operations in memory and in the on-disk journal after the changes are present in the data files on disk.

Note: This question has more than 1 correct answers

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155.

What is the maximum size of an Index key?

Answer

Correct Answer: 1024 bytes

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156.

What is the maximum number of Indexes per collection allowed?

Answer

Correct Answer: 64 indexes

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157.

Choose the best statement that describes:  "why aggregation queries outperform mapreduce for small datasets".

Answer

Correct Answer: There is a JavaScript lock so a mongod server can only execute one JavaScript function at a time

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158.

Which of the following expressions can not be used with aggregation?

Answer

Correct Answer: $pop

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159.

What will be the output of the following two commands in MongoDB: db.mycol.insert({"_id":1}) db.mycol.insert({"_id":1})

Answer

Correct Answer: This will throw duplicate key error

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160.

Choose the best description of the output for the query below var weekAgo = Date.now() - (1000*60*60*24*7); db.visits_calc.group( { key:{date:true}, cond:{date:{$gt:weekAgo}}, reduce:function(obj, out) {out.day += obj.total}, initial:{day:0} });

Answer

Correct Answer: Returns results for the last week grouped by day

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161.

Regarding data modeling in MongoDB, which of the following is correct ?

Answer

Correct Answer: All of the above

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162.

Which of the following commands will find all the posts that have been tagged as tutorial?

Answer

Correct Answer: db.posts.find({ tags: "tutorial" })

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163.

What kind of NoSQL database MongoDB is?

Answer

Correct Answer: Document Oriented

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164.

Which of the following are atomic operations in MongoDB?

Answer

Correct Answer: .remove
.findAndModify

Note: This question has more than 1 correct answers

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165.

Point out the wrong statement :

Answer

Correct Answer: Collections do enforce document structure

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166.

Which of the following is correct about Capped Collections?

Answer

Correct Answer: To make room for new documents, capped collections automatically remove the oldest documents in the collection without requiring scripts or explicit remove operations.
High-throughput operations that insert and retrieve documents based on insertion order.

Note: This question has more than 1 correct answers

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167.

What is the default size of GridFS chunk?

Answer

Correct Answer: 255 kB

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168.

Which one of the following is a primary key in MongoDB?

Answer

Correct Answer: _id

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169.

Which of the following methods can be used in MongoDB for relating documents?

Answer

Correct Answer: Both of the above

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170.

Which of the following is correct for _id in MongoDB?

Answer

Correct Answer: _id: ObjectId(4 bytes timestamp, 3 bytes machine id, 2 bytes process id, 3 bytes incrementer)

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171.

Which of the following collections are used by MongoDB to store GridFS data?

Answer

Correct Answer: fs.files and fs.chunks

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172.

What is Profiler?

Answer

Correct Answer: Profiler is used to show the performance characteristics of every operation against the database.

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173.

Which of the following is correct syntax for creating an index?

Answer

Correct Answer: db.mycol.createIndex({"title":1})

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174.

Which of the following is the most suitable advantage of using embedded documents?

Answer

Correct Answer: Improves read performance and allow to reading of data in a single request to the database.

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175.

Which of the following command inside aggregate command is used in MongoDB aggregation to filter the documents to pass only the documents that match the specified condition to the next pipeline stage?

Answer

Correct Answer: $match

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176.

In MongoDB, write operations are atomic at the (...........) level.

Answer

Correct Answer: document

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177.

Query shape consists of a combination of query, sort, and _____ specifications.

Answer

Correct Answer: projection

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178.

Which of the following operations will write the resulting documents of the aggregation pipeline to a collection in MongoDB?

Answer

Correct Answer: $out

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179.

What is the difference between Sharding and Replication ?

Answer

Correct Answer: Replication creates additional copies of the data and allows for automatic failover while Sharding allows for horizontal scaling of data writes by partitioning data across multiple servers.

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180.

Regarding MongoDB sharding, choose the correct statement:

Answer

Correct Answer: MongoDB distributes data, or shards, at the collection level

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181.

Why is sharding necessary?

Answer

Correct Answer: All of the above

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182.

Why Sharding?

Answer

Correct Answer: Local disk is not big enough
Vertical scaling is too rexpensive
Memory cant be large enough when active dataset is big

Note: This question has more than 1 correct answers

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183.

Which of the following describes best the concept of Sharding in MongoDB ?

Answer

Correct Answer: t's a method for storing data across multiple machines. MongoDB uses it to support deployments with very large data sets and high throughput operations.

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184.

Regarding MongoDB sharding, choose the incorrect statement:

Answer

Correct Answer: For hash-based sharding, MongoDB divides the data set into ranges determined by the shard key values to provide hash based partitioning.

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185.

Which of the following components exists in sharded cluster?

Answer

Correct Answer: All of the above

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186.

A query fails to return a complete result set on a sharded cluster. Choose the most probable reason

Answer

Correct Answer: All the members of the sharded cluster can not reach all the other members

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187.

_____ interface with client applications and direct operations to the appropriate shard or shards.

Answer

Correct Answer: Query Routers

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188.

Which of the following is true about sharding?

Answer

Correct Answer: Sharding uses horizontal scaling.

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189.

Choose the best commands to clone a collection to a sharded cluster from a developer machine.

Answer

Correct Answer: Both mongoimport and mongoexport have optional --host and --port parameters to import from / export to a remote server

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190.

What do you mean by sharding?

Answer

Correct Answer: Storing data records across multiple machines to meet the demands of data growth.

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191.

Choose the best description for the query below db.foo.find({ $text:{ $search:"text" } });

Answer

Correct Answer: match query for strings containing 'text'

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192.

Describe the output of the following mongo shell JavaScript: Object.keys(db.collection.findOne())

Answer

Correct Answer: Lists all the collection's keys

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193. What is command specifying for database path ?

Answer

Correct Answer: --dbpath

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194. Asume a users collections with the following fields: "_id", "username", "password", "email". At least one of the users has registered all of the fields. If you run both this queries: 1) db.users.find({}, {password: false, email: false}); 2) db.users.find({}, {_id: false, username: true}) Would the output be the same?

Answer

Correct Answer: No

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195. Suppose you have a collection foo with an index created using the statement db.foo.ensureIndex({a:1, b:-1, c:1}). Which of the following queries could use the index

Answer

Correct Answer: db.foo.find({b:1})

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196. By default, MongoDB allows up to _____ collections.

Answer

Correct Answer: 12,000

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197. Haystack Indexes are typically used to:

Answer

Correct Answer: Improve the performance of 2D geospatial queries

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198. What is the minimum number of mongod instances that may make up a replica set?

Answer

Correct Answer: 1

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199. MongoDB queries return a limited size (or "threshold") of results by default, usually:

Answer

Correct Answer: 101

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200. A property used to address servers based on their real-world locations is called:

Answer

Correct Answer: Data-center awareness

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201. You cannot use characters among /\. "*<>:|? in database names, in release version

Answer

Correct Answer: >=2.2

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202. In MongoDB's Geospatial Indexing, if you want to create & use index on EARTH, what is NOT TRUE?

Answer

Correct Answer: Specifying in key like { lat : -50, lon : 13 }

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203. You want to minus one to field foo, what should you use?

Answer

Correct Answer: { $inc : { foo : -1 } }

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204. What term is use to describe the order that a database stores documents on disk?

Answer

Correct Answer: natural order

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205. When a replica set election takes place which types of nodes can participate

Answer

Correct Answer: regular, hidden, and arbiters

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206. Which datum does MongoDB use for calculating geospatial coordinates?

Answer

Correct Answer: WGS84

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207. How many data types are available in MongoDB?

Answer

Correct Answer: 6

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208. Which of the following is not a BSON serialization type?

Answer

Correct Answer: Hash table

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209. Which of the following statements are true about the MongoDB Write Consistency model

Answer

Correct Answer: Strongly consistent by default, can be made eventually consistent

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210. Which of the following is the correct operation to query a document for both 'Football' and "Reading" within the interests data collected from a profile?

Answer

Correct Answer: db.profile.find({interests: {$all : ["Football", "Reading"] }})

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211. How many collections are created when use use gridfs to store large files

Answer

Correct Answer: 2

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212. What is the correct aggregation pipeline to prefix all the values of the 'name' column in the 'test' collection?

Answer

Correct Answer: db.test.aggregate([{ $project: { name: { $concat: ['prefix', '$name'] } } }]);

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213. If you have a compound index on multiple fields (a,b,c), you can use it to query on:

Answer

Correct Answer: (a), (a,b), or (a,b,c)

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214. What is the easiest way to do tasks like totaling or averaging field values in MongoDB newer versions?

Answer

Correct Answer: Use Aggregation Framework

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215. All writes in MongoDB Must go the primary

Answer

Correct Answer: True

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216. "read preference" affects how an application:

Answer

Correct Answer: Selects a replica set member to read from

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217. A Priority 0 or "passive" replica member:

Answer

Correct Answer: Cannot become a primary member

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218. "write concern" allows an application to:

Answer

Correct Answer: Observe the success or failure of database writes

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219. When a Capped Collection becomes full, and a new document is added:

Answer

Correct Answer: The oldest entry is overwritten with the new document

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220. Due to their default behavior, Capped Collections are ideal for storing:

Answer

Correct Answer: Non-vital, chronological records, like logs

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221. What do drivers use with protocol on the wire?

Answer

Correct Answer: BSON

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222. What is the extra space allocated to document on the disk to prevent moving a document when it grows as the result of update() operations.

Answer

Correct Answer: padding

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223. MongoDB document names cannot start with the characters:

Answer

Correct Answer: $ or .

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224. Which of the following binaries handles routing of sharded queries to the proper shard?

Answer

Correct Answer: mongos

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225. An operation is said to be "idempotent" if it is proven to:

Answer

Correct Answer: Produce consistent results over multiple runs, given the same input

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226. Which of the following is not a stage in the aggregation pipeline

Answer

Correct Answer: having

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227. Indexing

Answer

Correct Answer: Slows down writes that involve the index

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228. While replication provides data redundancy, journaling is also recommended because:

Answer

Correct Answer: It allows faster, more reliable recovery after a crash

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229. Which feature of mongoDB is used for data redundancy?

Answer

Correct Answer: Replica Sets

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230. MongoDB uses the acronym TTL to mean:

Answer

Correct Answer: Time To Live

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231. MongoDB can have indexes on Array Elements?

Answer

Correct Answer: True, MongoDB indexes each element of the array.

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232. What's the difference between `save()` and `insert()` in mongo shell?

Answer

Correct Answer: save() updates the document if if already exists (judges by if they already contains `_id`); inserts if it's new.

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233. Authentication in MongoDB is:

Answer

Correct Answer: Off by default.

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234. Which of the following atomic operations would you use to add a value to an array only if it does not already exist in the array?

Answer

Correct Answer: $addToSet

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235. When Storing large files in MongoDB one is encouraged to use...

Answer

Correct Answer: GridFS

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236. MongoDB's Replication can be in Master-Slave form or _______ form.

Answer

Correct Answer: Replica Sets

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237. The aggregation framework is most similar to which facility from the world of relational databases

Answer

Correct Answer: Group by

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238. True or False? MongoDB can have foreign keys.

Answer

Correct Answer: False

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239. In MongoDB V2.4, what type of JavaScript engine is used to execute all JavaScript on Mongo shell ?

Answer

Correct Answer: V8

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240. Which statement of the followings could NOT drop an index?

Answer

Correct Answer: db.myCollection.reIndex()

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241. Which feature of mongoDB is used to balance load among multiple machines?

Answer

Correct Answer: Sharding

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242. Indexes in mongodb are NOT good for:

Answer

Correct Answer: Collections which are write-intensive

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243. To atomically modify and return a single document from a collection, use:

Answer

Correct Answer: findAndModify()

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244. The core database operations in MongoDB are abbreviated as:

Answer

Correct Answer: CRUD

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245. The currently preferred replication method is called:

Answer

Correct Answer: Replica sets

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246. Which of the following are considered Core MongoDB operations?

Answer

Correct Answer: Create, Read, Update, Delete

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247. Which of the following statements are true about MongoDB

Answer

Correct Answer: MongoDB does not support transactions but operations are atomic.

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248. Which method should be used to create an index on a collection, if it does not already exist?

Answer

Correct Answer: ensureIndex()

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249. The map-reduce operation uses a temporary collection for data processing; The benefit of this behavior is that the operations:

Answer

Correct Answer: Can be performed concurrently on the same collection, without affecting the intermediate states

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250. To create an index for user_name field on user collection, which of the following is the correct syntax?

Answer

Correct Answer: db.user.ensureIndex({user_name:1});

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251. Which platform does MongoDB support?

Answer

Correct Answer: All of above

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252. When a journal file holds 1 gigabyte of data, MongoDB creates a new journal file?

Answer

Correct Answer: True

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253. Instead of tables, MongoDB stores data in structures called:

Answer

Correct Answer: Collections

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254. MongoDB supports UTF-8 for strings in stored objects and queries:

Answer

Correct Answer: Always

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255. Which of the following terms describe MongoDB?

Answer

Correct Answer: Document-oriented DBMS

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256. How can you optimize document storage?

Answer

Correct Answer: (All of these)

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257. The interactive "mongo" shell interface is based on:

Answer

Correct Answer: JavaScript

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258. This replication process is

Answer

Correct Answer: asynchronous

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259. You can write custom MapReduce functions in MongoDB using:

Answer

Correct Answer: Javascript

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260. Which of the following expressions are valid JSON documents?

Answer

Correct Answer: {Name: "Schoolify", url: 'www.schoolifybd.com'}

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261. What does MongoDB's Sharding provide?

Answer

Correct Answer: All of these

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262. Which of the following statement are true

Answer

Correct Answer: If you do not specify and _id when doing an insert, the driver will create one for you

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263. The MongoDB database is capable of:

Answer

Correct Answer: Atomic (per document) operations

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264. To perform a search on a collection, and obtain a cursor object for the results, use:

Answer

Correct Answer: find()

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265. MongoDB stores documents in structures called

Answer

Correct Answer: BSON objects

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266. TSV files should be expected to contain:

Answer

Correct Answer: Tab-separated text fields

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267. The binary log of transactions used to recover the database after a crash is called the:

Answer

Correct Answer: Journal

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268. In what language(s) is MongoDB supported?

Answer

Correct Answer: All of above.

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