mongodb-quiz.md

MongoDB

Q1. Which command adds members to the replica set from MongoDB shell?

• rs.add("<hostname>")
• replicaSetAdd("<hostname>")
• rs.insert("<hostname>")
• replica.add("<hostname>")

Q2. Which MongoDB shell command should you use to back up a database?

• restore
• backup
• mongobackup
• mongodump

Q3. Which shell query displays all citizens with an age greater than or equal to 21?

• db.citizens.select('WHERE age >= 21')
• db.citizens.where('age >= 21')
• db.citizens.find('WHERE age >= 21')
• db.citizens.find({age: {$gte: 21}})

Q4. What does a MongoDB collection consist of?

• data
• documents
• fields
• rows

Q5. Given an ObjectId in _id, how do you get the time it was created?

• getDateTime(_id)
• _id.createDate()
• _id.getTimestamp()
• _id.getDateTime()

Q6. Given a cursor named myCursor, which command returns a boolean value?

• myCursor.hasNext()
• myCursor.sort()
• myCursor.next()
• myCursor.find()

Q7. Which command returns a specific document in the user's collection?

• db.users.find({_id: 1})
• db.users.seek({_id: 1})
• db.users.query({_id: 1})
• db.query.users({_id: 1})

Q8. To import a JSON array into Mongo, what flags are needed with MongoDBimport?

• --type jsonArray
• --json
• --type json
• --jsonArray

Q9. Choose the shell command that connects to a MongoDB database.

• mongo
• mongod
• mongoconnect
• dbconnect

Q10. In the MongoDB shell, how can you tell if an index was used with a query?

• db.customers.find({lastName: 'smith'}).explain()
• db.customers.find({lastName: 'smith'}).perf()
• db.customers.find({lastName: 'smith'}).plan()
• db.customers.find({lastName: 'smith'}).usedIndex()

Q11. Suppose your aggregation pipeline terminated with an exception referring to exceeded memory limit. What is the best way to resolve the issue?

• Set useMemory to twice amount indicated in exception.
• Switch a 64 bit instance of MongoDB.
• Increase the memory of the MongoDB server.
• Set allowDiskUse to true.

Q12. What is the recommended way to delete a user?

• db.deleteUser("user")
• db.removeUser("user") DEPRECATED
• db.remove("user")
• db.dropUser("user")

Q13. What the primary database in a replica set fails, when does failover begin?

• once the primary has been down for 10 minutes
• once the primary reboots
• immediately
• after the administrator reboots the primary

Q14. What is the correct option to set up Kerberos when starting MongoDBd?

• --setParameter authenticationMechanisms=GSSAPI
• --setAuthentication=GSSAPI
• --setParam auth=K
• --setAuth method=Kerberos

Q15. What is the purpose of an arbiter in a replica set?

• It monitors replica set and sends email in case of failure
• It casts the tie-breaking vote in an election.
• It holds a backup copy of the database.
• It reboots the failed server.

Q16. You want to know how many types of items you have in each category. Which query does this?

• db.product.group({_id: "$category", count: {$sum:1}})
• db.product.aggregate($sum: {_id: "$category", count: {$group:1}})
• db.product.aggregate($group: {_id: "$category", count: {$sum:1}})
• db.product.aggregate($count: {_id: "$category", count: {$group:1}})

Q17. To restrict the number of records coming back from a query, which command should you use?

• take
• limit
• max
• skip

Q18. You have a collection named restaurants with the geographical information stored in the location property, how do you create a geospatial index on it?

• db.restaurants.createIndex({location: "2dsphere"})
• db.restaurants.geospatial({location: "2dsphere"})
• db.restaurants.createIndex("2dsphere":"location")
• db.restaurants.createIndex({geospatial: "location"})

Q19. How do you find documents with a matching item in an embedded array?

• db.customers.findmatch ({"jobs":"secretary"})
• db.customers.find ({"jobs:secretary"})
• db.customers.find ({"jobs":["secretary"]})
• db.customers.find ({"jobs":"secretary"})

Q20. Which query bypasses the first 5 customers and returns the next 10?

• db.customers.find({}, {skip: 5, limit: 10})
• db.customers.find({}.page(5).take(10))
• db.customers.find({}).skip(5).take(10)
• db.customers.find({}).skip(5).limit(10)

Q21. How do you create a text index?

• db.customers.createIndex({firstName, lastName})
• db.customers.createTextIndex({firstName, lastName})
• db.customers.createIndex({firstName: "text", lastName: "text"})
• db.customers.createText({firstName: 1, lastName: 1})

Q22. 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?

• db.customers.createIndex("lastName, firstName, ASC")
• db.customers.addIndex({lastName:"ASC", firstName: "ASC"})
• db.customers.newIndex({lastName:1, firstName:1})
• db.customers.createIndex({lastName:1, firstName: 1})

Q23. 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?

• Set the replace option to true.
• Use the replaceOne() command instead.
• You can't. Once set, the _id field cannot be changed.
• Use the updateOne() command instead.

Q24. A compound index allows you to _ ?

• Calculate interest quickly.
• Accomplish nothing, since compound indexes aren't allowed in Mongo.
• Use more than one field per index.
• Combine fields in different collations.

Reference

Q25. Why are ad-hoc queries useful?

• They do not have to use the same operators.
• You do not need to structure the database to support them.
• They autogenerate reports.
• They run faster than indexed queries.

Q26. How often do the members of a replica set send heartbeats to each other?

• every 2 minutes
• every 5 seconds
• every 2 seconds
• every 10 seconds

Q27. Which command returns all of the documents in the customers collection?

• db.customers.all();
• db.find().customers();
• db.customers.find();
• db.customers.show();

Q28. Given a cursor named myCursor, pointing to the customers collection, how to you get basic info about it?

• myCursor.stats()
• myCursor.dump()
• myCursor.info()
• myCursor.explain()

Q29. What is true about indexes?

• They speed up read access while slowing down writes.
• They secure the database from intruders.
• They speed up reads and writes.
• They speed up write access while slowing down reads.

Q30. What is the preferred format to store geospatial data in MongoDB?

• Latitude, longitude
• XML
• GeoJSON
• BSON

Q31. Which programming language is used to write MongoDB queries? (Alternative: In the MongoDB shell, what programming language is used to make queries?)

• Python
• JavaScript
• SQL
• TypeScript

Q32. You have two text fields in your document and you'd like both to be quickly searchable. What should you do?

• Create a text index on each field.
• MongoDB is not able to do this.
• Create a compound text index using both fields.
• Create a text index on one field and a single field index on the other.

Q33. To import a CSV file into MongoDB, which command should you issue?

• mongorestore
• mongoi
• upload
• mongoimport

Q34. In an MongoDB mapReduce command, the reduce function should _.

• access the database
• be called only when the key has a single value
• access the database only to perform read operations
• not access the data

Q35. On a newly created collection, which field will have an index?

• the name field
• the ObjectId field
• the _id field
• no field will have an index

Q36. 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?

• limit, skip, sort
• sort, limit, skip
• limit, sort, skip
• sort, skip, limit

Q37. You would like the stats() command to return kilobytes instead of bytes. Which command should you run?

• db.vehicle.stats(1024)
• db.vehicle.stats("kilobytes")
• db.vehicle.stats(true)
• db.vehicle.stats("kb")

Q38. You want to modify an existing index. What is the best way to do this?

• Use the reIndex() command to modify the index.
• Delete the original index and create a new index.
• Call the createIndex() command with the update option.
• Use the updateIndex() command.

Q39. You need to delete the index you created on the description field. Which command will accomplish this?

• db.vehicle.dropIndex("description_text")
• db.vehicle.dropIndex({"description":"text"})
• db.vehicle.removeIndex({"description":"text"})
• db.vehicle.removeIndex("description_text")

Q40. You would like to know how many different categories you have. Which query will best get the job done?

• db.vehicle.distinct("category")
• db.vehicle.unique("category")
• db.vehicle.distinct("category").count()
• db.vehicle.distinct("category").length

Note: count() works with find(...) but length works with distinct

Q41. From the MongoDB shell, how do you create a new document in the customers collection?

• db.customers.add({name: "Bob"})
• db.customers.save({name: "Bob"})
• db.customers.create({name: "Bob"})
• db.customers.new({name: "Bob"})

Q42. Which field is required of all MongoDB documents?

• _id
• _name
• ObjectId
• mongoDB is schema-less so no field is required

Q43. A MongoDB instance has at least what three files?

• data, namespace, and journal
• namespace, journal, and log
• journal, data, and database
• data, log, and journal

Q44. You'd like a set of documents to be returned in last name, ascending order. Which query will accomplish this?

• db.persons.find().sort({lastName: -1}}
• db.persons.find().sort({lastName: 1}}
• db.persons.find().sort({lastName: ascending}}
• db.persons.find().sort({lastName: $asc}}

Q45. What is NOT a standard role in MongoDB?

• restore
• read/write
• dbadmin
• delete collections

Reference

Q46. Which MongoDB shell command deletes a single document?

• db.customers.delete({_id: 1});
• db.customers.drop({_id: 1});
• db.drop.customers({_id: 1});
• db.customers.remove({_id: 1});

Note: db.collection.remove() is deprecated in the new mongosh. Use db.collection.deleteOne() or db.collection.deleteMany().

References: db.collection.remove() db.collection.delete()

Q47. Using the MongoDB shell, how do you remove the customer collection and its indexes?

• db.customers.remove({}).indexes();
• db.customers.remove({});
• db.customers.drop();
• db.customers.delete();

Q48. By default, applications direct their read operations to which member of the replica set?

• primary
• arbiter
• secondary
• backup

Q49. You need to get the names of all the indexes on your current collection. What is the best way to accomplish this?

• db.people.getName();
• db.people.reIndex({names: 1});
• db.people.getIndexKeys();
• db.people.getIndexes();

Note: An alternative method in the mongosh shell is listIndexes()

Reference

Q50. 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?

• Use the replaceMany() command instead
• Use the updateMulti() command instead
• Use the updateMany() command instead
• Set the global multi option to True

Note: An alternative method for db is .update()

Reference

Q51. To cleanly shut down MongoDB, what command should you use from the MongoDB shell?

• quit()
• exit()
• db.shutdownServer()
• db.shutdown()

Q52. Given a customer collection which includes fields for gender and city, which aggregate pipeline shows the number of female customers in each city? (Alternative: How can you view the execution performance statistics for a query?)

• db.members.aggregate([ {$match: {gender: "Female"}}, {$group: {_id: {city: "$city"}, number: {$sum: 1}}}, {$sort :{number: -1}}])
• db.members.find({$match: {gender: "Female"}}, {$group: {_id: {city: "$city"}, number: {$sum: 1}}}.$sort ({number: -1})
• db.members.find([ {$match: {gender: "Female"}}, {$group: {_id: {city: "$city"}, number: {$sum: 1}}}, {$sort :{number: -1}}])
• db.members.aggregate([ {$match: {gender: "Female"}}, {$sort :{number: -1}}])

Note: If you want to analyze the performance of a query use .explain("executionStats")

Reference

Q53. When no parameters are passed to explain(), what mode does it run in?

• wireTiger mode
• executionStats mode
• queryPlanner mode
• allPlansExecution mode

Q54. What is the correct query to find all of the people who have a home phone number defined?

• db.person.find({exists: 'homePhone'});
• db.person.exists({homePhone: true});
• db.person.find({homePhone: {$exists: true}});
• db.person.has('homePhone');

Q55. Which file in the MongoDB directly holds the MongoDB daemon?

• mongodb
• mongo-daemon
• daemon
• mongod

Q56. You have just secured your previously unsecured MongoDB server, but the server is still not requiring authentication. What is the best option?

• Restart the mongod process.
• Issue the secure() command.
• Issue the mongoimport command.
• Issue the authenticate() command.

Q57. What is the most accurate statement regarding MongoDB and ad hoc queries?

• [] MongoDB does not allow ad hoc queries; all queries require an index.
• Ad hoc queries are allowed only in the paid version.
• Ad hoc queries are allowed only through the ad hoc command.
• MongoDB allows ad hoc queries.

Note: You don't need an index to perform ad hoc queries. Only pick one choice Reference

Q58. In MongoDB, what does a projection do?

• allows you to do a calculation on the results
• allows you to run queries on the server
• allows you to select which fields should be in the return data
• allows you to format the results for a display

Q59. To remove a database and all of its records from MongoDB, what operator should you use?

• dropDatabase()
• removeAll()
• clear()
• deleteDatabase()

Q60. What option can be passed to start the MongoDB shell without connecting to a database?

• -db=null
• --shell-only
• --free
• -nodb

Q61. How can you improve the appearance of the output JSON that contains the _id?

• Use db.collection.set({$_id:pretty})
• Use db.collection.find().pretty()
• Use db.collection.format(numeric)
• Use $_id = value

Reference:

Q62. What happens to a Replica set oplog if it runs out of memory?

• The oplog will be saved on one of the secondary servers.
• The oplog is capped collection and can't run out of memory
• The MongoDB instance will fail
• The oplog will stop recording logging information

Argument:

Why "The oplog will be saved on one of the secondary servers." is wrong:

MongoDB applies database operations on the primary and then records the operations on the primary's oplog. The secondary members then copy and apply these operations in an asynchronous process. All replica set members contain a copy of the oplog, in the local.oplog.rs collection, which allows them to maintain the current state of the database.

Reasoning behind the right answer:

The oplog (operations log) is a special capped collection that keeps a rolling record of all operations that modify the data stored in your databases.

Unlike other capped collections, the oplog can grow past its configured size limit to avoid deleting the majority commit point.

Q63. MongoDB ships with a variety of files. Which file runs the MongoDB shell?

• mongo
• mongo-s
• shell
• mongo-shell

Note: mongosh is the new mongo shell, mongo is deprecated.

Starting in MongoDB v5.0, mongosh replaces mongo as the preferred shell.

[Reference:] (https://www.mongodb.com/docs/mongodb-shell/)

Q64. How can you view the execution performance statistics for a query?

• db.performance.members.aggregate([ {$match: {gender: "Female"}}, {$group: {_id:{city:"$city"}, number: {$sum: 1}}}, {$sort : {number: -1}}])
• db.members.aggregate([ {$match: {gender: "Female"}}, {$group: {_id: {city: "$city"}, number:{$sum:1}}}, {$sort: {number:-1}}]).explain("executionStats")
• db.members.aggregate([ {$match: {gender: "Female"}}, {$group:{_id: {city: "$city"}, number: {$sum: 1}}}, {$sort: {number: -1}}]).explain()
• db.members.aggregate([ {$match: {gender: """Female"""}}, {$group: {_id: {city: """$city"""}, number: {$sum:1}}}, {$sort: {number: -1}}]).number()

Q65. From the MongoDB shell, how do you execute a JavaScript file named list.js?

• node 'list.js'
• exec('list.js)
• run('list.js)
• load('list.js)

Q66. Which MongoDB shell query will sort the customer's collection by name descending?

• db.customers.sort({name: -1}.find({})
• db.customers.sort({name: -1})
• db.customers.find({}).sort({name: -1})
• db.customers.find({}).sort({name: 1})

Q67. 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?

• The import command aborts without importing any records.
• The import command imports records upto but not including the record, and then aborts.
• The import command doesn't import the bad document but does import the rest.
• The import command prompts you to correct the bad record.

Note: By default, mongoimport continues an operation when it encounters duplicate key and document validation errors.

Reference

Q68. You have a collection with millions of documents. Each time you attempt to sort. MongoDB runs out of memory. What might help?

• Use the purge operator before the sort.
• Return the entire collection and sort on the client.
• Pass the --more-memory option.
• Create an index on the field you are sorting.

Q69. You need to be able to quickly find a word in a text field. What should you do?

• Create a text index on the field and do a $text Query.
• Create a single field index in descending order, and do a query for the word.
• Do a $text query.
• Create a $regex on the fields, and do a $regex query.

Argument: You need a text index in order to perform a $text query on a field. $text query uses the text index under the hood

References: $text query Text index

Q70. Which field is always included in a projection unless specifically excluded?

• index
• Name
• _id
• row number

Reference

Q71. After installing MongoDB on your machine, what must you do before launching Mongo?

• Create a user account.
• Register online.
• Create a data directory.
• Establish security credentials.

Note: The question in case is ambiguous. In the mongo docs, on the Windows Installation section, it clearly specifies the need for creating a data directory. However, that does not seem to be the case for Unix based systems. So, that gives use the closest possible solution for a specific platform. If we extrapolate that to the question, that seems to be the most reasonable solution.

mongodb site

Q72. How does a --jsonArray file need to be structured?

• as a properly formatted JSON array
• as YAML
• as plain text
• as a BSON object

Section blog

Q73. From the MongoDB shell, how do you display all of a database's memory usage?

• db.size()
• db.info()
• db.memory()
• db.stats()

Q74. How do you create a new MongoDB user?

• db.createUser({})
• db.insert({user: 1})
• db.customers.newUser({})
• db.newUser({})

MongoDB documentation

Q75. What is the internal data structure of a MongoDB document?

• JSON (JavaScript Object Notation)
• BSON (Binary JSON)
• ORM (object relational mode)
• MBF (MongoDB binary format)

MongoDB documentation JSON and BSON

Q76. Which projection shows only the FirstName and lastName fields of a document in the customers collection?

• db.customers.find({}, {firstName: 1, lastName: 1})
• db.customers.find({}, {_id:0, firstName: 1, lastName: 1})
• db.customers.find({_id: 0, year: 1, maek: 1, model: 1})
• db.customers.find({}).project({firstName: 1, lastName: 1})

Q77. Documents in mongodb are atomic at the ___ level

• database
• field
• no
• document

MongoDB reference

Q78. What should the priority of a member be in order to prevent it from becoming the primary in replica set?

• 1
• null
• 0
• -1

MongoDB reference

Q79. 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?

• Use the reIndex() command to add the index quickly.
• Use the createIndex() command with the option background = true.
• Use the createIndex() command.
• Use the createIndex() command with the option parallel = true.

MongoDB reference

Concurrency Changed in version 4.2.

MongoDB uses an optimized build process that obtains and holds an exclusive lock on the specified collection at the start and end of the index build. All subsequent operations on the collection must wait until createIndex() releases the exclusive lock. createIndex() allows interleaving read and write operations during the majority of the index build.

For more information on the locking behavior of createIndex(), see Index Builds on Populated Collections.

Q80. When using aggregation $convert. which is not a parameter?

• input
• output
• to
• onError

MongoDB reference

Q81. All tag values in tag sets must be _.

• JSON
• integers
• strings
• XML

MongoDB reference

Q82. When using the mongoimport command, how can you drop the database before importing?

• Use the -d option.
• Use the mongooverwrite command instead of mongoimport.
• Use the -drop option.
• Drop the database manually before importing.

Argument: There is no -d option in the docs (https://www.mongodb.com/docs/database-tools/mongoimport/#options.)

Note: Assuming you are asked to drop a collection instead while importing, the use the --drop option.

Q83. To import a CSV file into MongoDB, which command should you issue?

• upload
• mongorestore
• mongoi
• mongoimport

Q84. A critical record must be replicated to the two other servers in the set. Which query guarantees that it is inserted as desired?

• db.inventory.insert({ prodid: "tab1122", qty : 10}, { writeConcern: { w: 2, wtimeout: 5000} })
• db.inventory.insert({ prodid: "tab1122", qty : 10}, { writeConcern: { j: true} })
• db.inventory.insert({ prodid: "tab1122", qty : 10}, { writeConcern: { w: 2, j:false, wtimeout: 5000} })
• db.inventory.insert({ prodid: "tab1122", qty : 10}, { writeConcern: { w: 2, j:true, wtimeout: 5000} })

MongoDB reference

Q85. What is the name of the default file used to configure MongoDB?

• mongo.config
• mongod.conf
• config.sys
• .mdbconfig

MongoDB reference

Q86. After using the dropIndexes() command on your collection, one index remains.What can you do to drop the the remaining index?

• Use dropIndexes({all:1}) with the all parameter.
• The required_id index cannot be deleted.
• Call dropIndex({"id":1}) to force its removal.
• Call dropIndex({"id"}) to force its removal.

MongoDB reference

Q87. To scale horizontally, what does MongoDB use?

• sharding
• replication
• partition
• backup

MongoDB reference

Q88. Your database collection holds web session information. One field, lastActivity, holds the timestamp of when the user was last active. You want to delete the user session after 30 minutes of inactivity. What is your best option?

• Create Javascript function called via an interval timeout to delete all records older than 30 minutes.
• Create a TTL index on the lastActivity field and set expireAfterSeconds to 1800.
• You have to create a stored procedure.
• Every time you create a new record for expired older records and delete them.

MongoDB reference