Mongo

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

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

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.

How many members a replica set can have?

Answers:

• Up to 10

• Up to 25

• Up to 50

• Up to 100

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

What is the minimum nodes required for replica?

Answers:

• 2

• 3

• 1

• No minimum required

Sometimes the failover process may require a ____ during operation.

Answers:

• savepoint

• rollback

• commit

• None of the above

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

Which of following helps analyze a query?

Answers:

• understand

• analyze

• explain

• executionInfo

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

Which of the following are atomic operations in MongoDB?

Note: There may be more than one right answer.

Answers:

• .findOne

• .findById

• .remove

• .findAndModify

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

Answers:

• Read operations

• Write operations

• Cursor Operations

• All of the above

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

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

Answers:

• Hbase

• Hive

• Map-reduce

• None of the mentioned

Which of the following are correct index types?

Answers:

• Compound

• Geospatial

• TTL

• All of the above.

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.

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

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»,

}

{

patron_id: «joe»,

street: «123 Fake Street»,

city: «Faketon»,

state: «MA»,

zip: «12345»

}

Answers:

• {

_id: «joe»,

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»,

address:: {

street: «123 Fake Street»,

city: «Faketon»,

state: «MA»,

zip: «12345»

}

• All of the above

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 }

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})

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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’

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

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

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» } )

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

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

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

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” }

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

Answers:

• .maxTime(1)

• .maxScan(1)

• .maxTimeMS(1000)

• .maxTimeMS(1)

Which of the following methods will shut down replica set?

Answers:

• newReplica.stop();

• newReplica.stopSet();

• newReplica.stopSets();

• newReplica.downSet();

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

Why use Replication?

Answers:

• To keep your data safe

• Disaster Recovery

• Read scaling

• All of the above

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

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

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 process on which MongoDB preallocates data files to reserve space and avoid file system fragmentation when you setup the server.

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

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.

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

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

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.

What is the default size of GridFS chunk?

Answers:

• 2 MB

• 255 kB

• 1 MB

• 16 MB

What kind of NoSQL database is MongoDB?

Answers:

• Graph

• Key Value

• Document Oriented

• Column Oriented

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

Which of the following fields does DBRefs have?

Answers:

• $ref

• $id

• $db

• All of the above

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» })

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()

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

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

Answers:

• collection

• document

• raw

• All of the above

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

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

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

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.

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

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

Answers:

• createdAt

• updatedAt

• _id

• None of the Above

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

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

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

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

Answers:

• hint

• haxNext

• next

• snapshot

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

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

Which of the following are stages of aggregation?

Note: There may be more than one right answer.

Answers:

• $sort

• $skip

• $drop

• $limit

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

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

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

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 } } );

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

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.

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

Which of the following components exists in sharded cluster?

Answers:

• Mongos

• Shard

• Config servers

• All of the above

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

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

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.

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

Answers:

• 1

• 2

• 3

• 4

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

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

What is the maximum number of Indexes per collection allowed?

Answers:

• 1024 indexes

• unlimited indexes

• 64 indexes

• No limit

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

Answers:

• plan

• shape

• stats

• None of the above.

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’

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

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

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

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

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

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

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

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

Answers:

• $addToSet

• $pop

• $push

• $sum

What is the maximum size of an Index key?

Answers:

• 12 mega bytes

• 16 mega bytes

• 1024 bytes

• None of the above

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

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

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}]);

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.

niten2/upwork_mongo.md

Mongo

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