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MongoDB Test 2018

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91 Test Questions:

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

Answers:

• New databases will be assigned a primary on the «most available» shard where most available means the shard with the least amount of data on it
• Each shard in MongoDB is its own mongod, an isolated MongoDB in itself (Every shard in MongoDB is its own mongod)
• By Implementing replicating sets
• The query routers distribute the load to compensate for shard endpoint resources

2. 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:

Answers:

• You have not run rs.initiate() in the master node
• You need to run reconfig in the master node
• You have not run rs.initiate() in the master node and rs.slaveOk() on the secondaries
• Your rs.add(«….») is missing the quotation marks

3. Which of the following is true about replica set?
Note: There may be more than one right answer.

Answers:

• It’s a group of servers with one primary.
• It’s a group of servers with many primaries.
• It’s a group of servers with one secondary.
• It’s a group of servers with many secondaries.

4. How many members a replica set can have?

Answers:

• Up to 10
• Up to 25
• Up to 50
• Up to 100

5. Point out the correct statement :

Answers:

• A rollback does not occur if the write operations replicate to another member of the replica set before the primary steps down
• Secondaries that can not keep up with the throughput of operations on the former primary, decrease the size and impact of the rollback
• Fault tolerance is an effect of replica set size, but the relationship is not direct
• None of the mentioned

6. What is the minimum nodes required for replica?

Answers:

• 2
• 3
• 1
• No minimum required

7. Sometimes the failover process may require a ____ during operation.

Answers:

• savepoint
• rollback
• commit
• None of the above

8. What is the use of profiler?

Answers:

• Profiler is used to execute every operation used in the query.
• Profiler is used to show the performance characteristics of every operation against the database.
• Profiler is used to optimize the data model of the database.
• None of the above

9. Which of following helps analyze a query?

Answers:

• understand
• analyze
• explain
• executionInfo

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

Answers:

• Will sort in descending numerical order
• Returns the last 50 entries in descending order
• Fails as the limit operator should precede the sort operator
• Returns the last 50 entries in ascending order

11. Which of the following are atomic operations in MongoDB?
Note: There may be more than one right answer.

Answers:

• .findOne
• .findById
• .remove
• .findAndModify

12. Which of the following information is captured by the Database Profiler in MongoDB ?

Answers:

• Read operations
• Write operations
• Cursor Operations
• All of the above

13. Choose the best statement «why aggregation queries out perform mapreduce for small datasets».

Answers:

• MapReduce functions are written in JavaScript
• Aggregation is able to use indexes and internal optimizations
• MapReduce is optimised for sharded input collections
• There is a JavaScript lock so a mongod server can only execute one JavaScript function at a time

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

Answers:

• Hbase
• Hive
• Map-reduce
• None of the mentioned

15. Which of the following are correct index types?

Answers:

• Compound
• Geospatial
• TTL
• All of the above.

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

Answers:

• It’s a method for storing data across multiple machines. MongoDB uses it to support deployments with very large data sets and high throughput operations.
• 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.
• 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.
• It’s the process on which MongoDB preallocates data files to reserve space and avoid file system fragmentation when you setup the server.

17. Why is sharding necessary?

Answers:

• In replication all writes go to master node.
• Memory can’t be large enough when active data set is big.
• Local disk is not big enough.
• Vertical scaling is too expensive.
• All of the above

18. 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»
}

Answers:

• {
_id: «joe»,
name: «Joe Bookreader»,
address: {
street: «123 Fake Street»,
city: «Faketon»,
state: «MA»,
zip: «12345»
}
}

• {
_id: «joe»,
name: «Joe Bookreader»,
address-> {
street: «123 Fake Street»,
city: «Faketon»,
state: «MA»,
zip: «12345»
}
}

• {
_id: «joe»,
name: «Joe Bookreader»,
address:: {
street: «123 Fake Street»,
city: «Faketon»,
state: «MA»,
zip: «12345»
}
}

• All of the above

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

Answers:

• { x: 1 }
• { x: 1, y:1, z: 1 }
• { x: 1, z: 1 }
• { x: 1, z: -1 }

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

Answers:

• db.stats({collection: user})
• db.user.stats()
• db.user.findStats()
• db.user.find({stats:1})

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

Answers:

• case insensitive match query
• case sensitive match query with pretty italics
• case insensitive query for those users whose name has ‘m’
• case insensitive query for those users whose name starts with ‘m’

22. Regarding MongoDB sharding, choose the correct statement:

Answers:

• MongoDB distributes data, or shards, at the collection level
• To shard a document, you need to select a shard key
• MongoDB divides the shard key values into replica sets
• All of the mentioned

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

Answers:

• The key decision in designing data models for MongoDB applications revolves around the structure of documents and how the application represents relationships between data.
• There are two tools that allow applications to represent these relationships: references and embedded documents.
• When designing data models, always consider the application usage of the data (i.e. queries, updates, and processing of the data) as well as the inherent structure of the data itself.
• All of the above

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

Answers:

• db.album.songs.insert( { title: «Roar», artist: «Katy Perry» } )
• db.album.insert( { title: «Roar», artist: «Katy Perry» } )
• album.songs.insert( { title: «Roar», artist: «Katy Perry» } )
• db.songs.insert( { title: «Roar», artist: «Katy Perry» } )

25. Which of the following may be a use case where MongoDB is a good fit?

Answers:

• When you need to prevent data duplication
• When you need strong referential integrity
•When you need to store data with nested arrays
• When you need to optimise resources

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

Answers:

• Both mongoimport and mongoexport and copy the file to the destination server with correct authentication
• mongodump and mongorestore to export the data in bson format
• Both mongoimport and mongoexport and copy the file to the destination server. In a securely configured network, you shouldn’t be able to access both developer and production database from the same machine
• Both mongoimport and mongoexport and copy the file to the destination server with correct authentication

27. Regarding MongoDB sharding, choose the incorrect statement:

Answers:

• For hash-based sharding, MongoDB divides the data set into ranges determined by the shard key values to provide hash based partitioning.
• cloud-based providers may only allow users to provision smaller instance.
• For hash based partitioning, MongoDB computes a hash of a field’s value, and then uses these hashes to create chunks.
• All of the above

28. 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.

Answers:

• { “field1” : “val1”, field2 : [“val2”] }
• { field1 : [“val1”], field2: {“field3”:…} }
• { field1: {“field2”:…} , field3: {“field4”:…} }
• { “field1” : “val1”, “field2” : “val2” }

29. Which of the following calls will set 1 second limit for a query?

Answers:

• .maxTime(1)
• .maxScan(1)
• .maxTimeMS(1000)
• .maxTimeMS(1)

30. Which of the following methods will shut down replica set?

Answers:

• newReplica.stop();
• newReplica.stopSet();
• newReplica.stopSets();
• newReplica.downSet();

31. Point out the wrong statement :

Answers:

• In all cases, you can use replication to increase read capacity
• Clients have the ability to send read and write operations to different servers
• You can also maintain copies in different data centers to increase the locality and availability of data for distributed applications
• None of the mentioned

32. Why use Replication?

Answers:

• To keep your data safe
• Disaster Recovery
• Read scaling
• All of the above

33. 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?

Answers:

• netLatency
• primaryPreferred
• nearest
• secondaryPreferred

34. 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:

Answers:

• Use the —dbpath parameter to point to the new partition
• Just move your folder, add symlink, then tune permissions
• Change the settings in mongod.cfg
• Change the settings in mongod.conf

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

Answers:

• It’s a method for storing data across multiple machines. MongoDB uses it to support deployments with very large data sets and high throughput operations.
• 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.
• 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.
• It’s the process on which MongoDB preallocates data files to reserve space and avoid file system fragmentation when you setup the server.

36. The oplog (operations log) in MongoDB is a special capped collection that keeps a rolling record of all operations that modify the data stored in your databases. All the replica set members contain a copy of the oplog in the _____ collection.

Answers:

• oplog.rs
• local.oplog.rs
• .oplog.rs
• None of the above

37. What is the difference between Sharding and Replication ?

Answers:

• Replication allows for horizontal scaling of data writes by partitioning data across multiple servers while Sharding creates additional copies of the data.
• 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.
• Replication allows for horizontal scaling of data writes by partitioning data across multiple servers using a replication parameter while Sharding creates additional copies of the data and allows for automatic failover using a shard key.
• Replication creates copies of the working set while Sharding distributes queries in parallel across mongod instances.

38. 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?

Answers:

• major
• n
• majority
• m

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

Answers:

• newReplica = new ReplSetTest(3);
• newReplica = new ReplSetTest({nodes:3});
• newReplica = new ReplSetTest();
• newReplica = new ReplSetTest(null);
• None of the above

40. Which of the following is true? Check all that applies.
Note: There may be more than one right answer.

Answers:

• A replica set is a group of mongodb instances that host the same data set.
• Replica set has only one node.
• In a replica one node is primary node that receives all write operations.
• At the time of automatic fail over or maintenance, all secondary nodes act as main node.
• Some data replicates from primary to secondary node.

41. What is the default size of GridFS chunk?

Answers:

• 2 MB
• 255 kB
• 1 MB
• 16 MB

42. What kind of NoSQL database is MongoDB?

Answers:

• Graph
• Key Value
• Document Oriented
• Column Oriented

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

Answers:

• Defaults to the guid for objects system keys
• Lists all the collection’s keys
• Returns an error as the key space is not defined for a schema-less design
• Returns an error as you can only check for the existence of a field

44. Which of the following fields does DBRefs have?

Answers:

• $ref
• $id
• $db
• All of the above

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

Answers:

• db.posts.find({ tags: [«tutorial»] })
• db.posts.find({ $array: {tags: «tutorial»} })
• db.posts.find({ tags: «tutorial» })
• db.posts.findInArray({ tags: «tutorial» })

46. 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.

Answers:

• Project the creation date
• Projection with ObjectId.getTimestamp()
• Map the projection with ObjectId.getTimestamp()
• Aggregate the collection with ObjectId.getTimestamp()

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

Answers:

• Usability reasons
• One-to-many relationships
• ‘contains’ relationships between entities
• When there are so many embedded document updates that it becomes a bottleneck for performance

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

Answers:

• collection
• document
• raw
• All of the above

49. Which of the following is correct for _id in MongoDB?

Answers:

• _id: ObjectId(4 bytes timestamp, 3 bytes machine id, 2 bytes process id, 3 bytes incrementer)
• _id: ObjectId(3 bytes machine id, 2 bytes process id, 3 bytes incrementer, 4 bytes timestamp)
• _id: ObjectId(2 bytes process id, 3 bytes incrementer, 4 bytes timestamp, 3 bytes machine id)
• _id: ObjectId(4 bytes timestamp, 3 bytes machine id, 3 bytes incrementer, 2 bytes process id)
• None of the Above

50. Which of the following is a valid MongoDB document?

Answers:

• {«user_name:»John»}
• {}
• {«user_name»=»John»}
• {«user_name»:»John», category:[«first»:»IT», «second»:»Networking»]}
• None of the above

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

Answers:

• Will sort in ascending order by _id
• Will sort oldest to newest as _id includes a date object
• Will project the id field in a natural sort
• Will sort in ascending numerical order based on the hash for the id field

52. Which of following points describes the use of embedded data models?

Answers:

• One-to-many relationships.
• Many-to-many-relationships.
• To have better performance.
• One-to-many relationships. Many-to-Many relationships.

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

Answers:

• It allows reading connected data in a single request to the database.
• Saves on indexing resources
• Improves write performance as is denormalizing
• Leads to easier projection queries

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

Answers:

• createdAt
• updatedAt
• _id
• None of the Above

55. Which of the following is correct about Capped Collections? (choose all that apply)
Note: There may be more than one right answer.

Answers:

• To make room for new documents, capped collections automatically removes 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.
• Capped collections do not guarantee preservation of the insertion order.
• All of the above

56. Which collection is used by MongoDB to store GridFS data?

Answers:

• fs.grid and fs.parts
• fs.files and fs.chunks
• fs.parts and fs.files
• None of the above

57. Which of the following parameters affect ObjectId? (choose all that apply)
Note: There may be more than one right answer.

Answers:

• Internet connection
• Timestamp
• Machine ID
• Client browser’s process ID

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

Answers:

• hint
• haxNext
• next
• snapshot

59. Which statement best describes $allElementsTrue?

Answers:

• Evaluates an array as a set and returns true if no element in the array is false
• Evaluates an array as a set and returns true if no element in the array is null
• Evaluates an array as a set and returns true if no element in the array is false. If the array contains a nested array then it performs the same operation on the nested array
• 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

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

Answers:

• $match
• $project
• $group
• $aggregate

61. Which of the following are stages of aggregation?
Note: There may be more than one right answer.

Answers:

• $sort
• $skip
• $drop
• $limit

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

Answers:

• $in
• $out
• $output
• None of the above

63. Regarding Pipeline Operators in MongoDB, which of the following is an incorrect statement? (choose all that apply)
Note: There may be more than one right answer.

Answers:

• $avg is an accumulator operator available only in the $group stage
• $avg is an accumulator operator available only in the $project stage
• $avg ignores non-numeric values
• All of the mentioned are correct statements

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

Answers:

• db.mycol.createIndex({«title»:1})
• db.mycol.create({«title»:1})
• db.mycol.makeIndex({«title»:1})
• All of the above

65. 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 ?

Answers:

• db.posts.find({ likes : { $gt : 100, $lt : 200 } } );
• db.posts.find({ likes : { $gte : 100, $lt : 200 } } );
• db.posts.find({ likes : { $gt : 100 , $lte : 200 } } );
• db.posts.find({ likes : { $gte : 100 , $lte : 200 } } );

66. When is sharding needed? (choose all that apply)
Note: There may be more than one right answer.

Answers:

• Local disk is not big enough
• Single replica set has limitation of 10 nodes
• Vertical scaling is too expensive
• Memory can’t be large enough when the active dataset is big

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

Answers:

• It’s a method for storing data across multiple machines. MongoDB uses it to support deployments with very large data sets and high throughput operations.
• 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.
• It’s the operation that processes data records and returns 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.
• It’s the process on which MongoDB preallocates data files to reserve space and avoid file system fragmentation when you setup the server.

68. Which of the following are strategies of Sharding?
Note: There may be more than one right answer.

Answers:

• Hashed
• Ranged
• Key
• All of the above

69. Which of the following components exists in sharded cluster?

Answers:

• Mongos
• Shard
• Config servers
• All of the above

70. Which statement is valid?

Answers:

• Sharding occurs on database level.
• Sharding occurs at the index level.
• MongoDB shards data at the collection level.
• None of the above

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

Answers:

• You need to update the ShardVersion system property
• One of the Mongodb processes has a system lock
• All the members of the sharded cluster can not reach all the other members
• You need to increase the number of replica sets

72. Which of the following is true about sharding?

Answers:

• Sharding is the method of horizontal scaling.
• Sharding allows adding maximum of 10 machines.
• Sharding is the method of vertical scaling.
• Replication and Sharding are the same.

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

Answers:

• 1
• 2
• 3
• 4

74. What do you mean by sharding?

Answers:

• Storing data records across multiple machines to meet the demands of data growth.
• Process of synchronizing data across multiple servers.
• Process of processing data records and returning computed results.
• None of the above

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

Answers:

• db.COLLECTION_NAME.ensureIndex({ KEY: 1 })
• COLLECTION_NAME.ensureIndex({ KEY: 1 })
• db.COLLECTION_NAME.createIndex({ KEY: 1 })
• None of the Above

76. What is the maximum number of Indexes per collection allowed?

Answers:

• 1024 indexes
• unlimited indexes
• 64 indexes
• No limit

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

Answers:

• plan
• shape
• stats
• None of the above.

78. Choose the best description for the query below

db.foo.find({
$text:{
$search:»text» }
});

Answers:

• match query for strings containing ‘text’
• match query for strings like ‘text’
• match query for tokens containing ‘text’
• match query for tokens like ‘text’

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

Answers:

• The query returned 30000 documents after scanning the documents
• The query used an index to fetch the results
• The query returned 0 documents
• None of the above

80. Which of the following methods allow you to insert documents into a collection?(choose all that apply)
Note: There may be more than one right answer.

Answers:

• insert
• insertSingle
• insertOne
• insertMany

81. What is a covered query?

Answers:

• It uses at least some of the index
• It returns all fields in the document
• The 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
• None of the above

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

Answers:

• $unwind
• $select
• $selectFields
• $project

83. What can be done to optimize aggregation pipeline?

Answers:

• Place the $match as early in the aggregation pipeline as possible
• Place the $match as the second argument in the aggregation pipeline and place first $group
• Use $where in $match queries as part of the aggregation pipeline
• Use $text in $match stage when $match is last argument in pipeline

84. Which of the following is not an aggregation operation? (choose all that apply)
Note: There may be more than one right answer.

Answers:

• Sum
• Average
• Max
• Update
• Min
• Insert

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

Answers:

• If you only ever query on a single key in a given collection, then you need to create just multikey index for that collection
• 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
• The choice between creating compound indexes that support your queries or relying on index intersection is independent of specifics of your system
• None of the mentioned

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

Answers:

• $addToSet
• $pop
• $push
• $sum

87. What is the maximum size of an Index key?

Answers:

• 12 mega bytes
• 16 mega bytes
• 1024 bytes
• None of the above

88. Which statement best describes the query below?

db.col1.findAndModify({
query: {«name»: «val1»},
update: { $inc: { «subObj.field1»: 1 } });

Answers:

• Returns a collection of documents where name is val1
• Returns a single document where name is val1 and field1 incremented by 1 in the returned document
• Returns a single document where name is val1 and field1 is unmodified in the returned document
• Returns a collection of documents where name is val1 and field1 incremented by 1

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

Answers:

• If your collection name includes the null character
• If your collection name includes the underscore character
• If your collection name includes the system. Prefix
• If your collection name is greater than 160 bytes

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

Answers:

• db.users.aggregate({$match: {name: «John»}}).sort({age: -1}).limit(1);
• db.users.aggregate({$select: {name: «John»}}, {$sort: {age: -1}}, {$limit: 1});
• db.users.aggregate({$select: {name: «John»}}, {$sort: {age: -1}}).limit(1);
• db.users.aggregate([{$match: {name: «John»}}, {$sort: {age: -1}}, {$limit: 1}]);

91. Regarding storage in MongoDB, which of the following statements are incorrect?
Note: There may be more than one right answer.

Answers:

• 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.
• A storage engine is the part of a database that is responsible for managing how data is stored on disk. For example, one storage engine might offer better performance for read-heavy workloads, and another might support a higher-throughput for write operations.
• MongoDB can use MMAPv1 or WiredTiger as Storage Engine
• 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.