Introduction to Mongo Database Interview Questions and Answers
So if you have finally found your dream job in Mongo Database but are wondering how to crack the 2018 Mongo Database Interview and what could be the probable Mongo Database Interview Questions. Every interview is different and the scope of a job is different too. Keeping this in mind we have designed the most common 2018 Mongo Database Interview Questions and Answers to help you get success in your interview.
Following are the Mongo Database Interview Questions that will help you for cracking an interview with maven. These Questions are divided into two parts are as follows:
Part 1 – Mongo Database Interview Questions
This first part covers basic Mongo Database Interview Questions and Answers.
1. Mention the type of Mongo Database and explain?
Answer:
Mongo Database is a document-oriented database, not a relational one the primary reason For moving away from the relational model is to make scaling out easier. A document-oriented database replaces the concept of a “row” with a more flexible model, the “document” By allowing embedded documents and arrays. The document-oriented approach makes it possible to represent complex hierarchical relationships with a single record. This fits naturally into the way developers in modern object-oriented languages.
2. Mention the unique feature of Mongo Database?
Answer:
Indexing: MongoDB supports generic secondary indexes, allowing a variety of fast queries and provides unique, compound, geospatial and full-text indexing capabilities as well.
Aggregation: MongoDB supports an “aggregation pipeline” that allows you to build complex aggregations from simple pieces and allow the database to optimize it.
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Special collection types: MongoDB supports time-to-live collections for data that should expire at a certain time, such as sessions. It also supports fixed-size collections, which are useful for holding recent data, such as logs.
File storage: MongoDB supports an easy-to-use protocol for storing large files and file metadata.
Some features common to relational databases are not present in MongoDB, notably joins and complex multi-row transactions. Omitting these was an architectural decision to allow for greater scalability, as both of those features are difficult to provide efficiently in a distributed system.
3.What is the command for getting started with MongoDB?
Answer:
mongod
mongod –help for help and startup options
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4. How do you represent null value in a variable in MongoDB?
Answer:
{"x" : null}
5.write down the code to connect to MongoDB
Answer:
var connectTo = function(port, dbname)
{
if (!port) {
port = 27017;
}
if (!dbname) {
dbname = "test";
}
db = connect("localhost:"+port+"/"+dbname);
return db;
};
6. What is GridFs in MongoDB?
Answer:
GridFS is a mechanism for storing large binary files in MongoDB.
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7. What are the benefits of Mondo DB?
Answer:
There are many benefits of MongoDB some of the features such as Using GridFS can simplify your stack. If you’re already using MongoDB, you might be able to use GridFS instead of a separate tool for file storage.GridFS will leverage any existing replication or auto-sharding that you’ve set up for MongoDB, so getting failover and scale-out for file storage is easier. GridFS can alleviate some of the issues that certain file-systems can exhibit when being used to store user uploads. For example, GridFS does not have issues with storing large numbers of files in the same directory.
8. Write down the syntax for string expression in MongoDB?
Answer:
"$substr" : [expr, startOffset, numToReturn]
9. What is MapReduce in MongoDB?
Answer:
MapReduce is a powerful and flexible tool for aggregating data. It can solve some problems that are too complex to express using the aggregation framework’s query language. MapReduce uses JavaScript as its “query language” so it can express arbitrarily complex logic. MapReduce tends to be fairly slow and should not be used for real-time data analysis.
Part 2 – Mongo Database Interview Questions (Advanced)
Let us now have a look at the advanced Mongo Database Interview Questions
10. Write the difference between Normalization and Denormalization?
Answer:
Normalization is dividing up data into multiple collections with references between collections. Each piece of data lives in one collection although multiple documents may reference it. Thus, to change the data, only one document must be updated. However, MongoDB has no joining facilities, so gathering documents from multiple collections will require multiple queries.
Denormalization is the opposite of normalization: embedding all of the data in a single document. Instead of documents containing references to one definitive copy of the data, many documents may have copies of the data. This means that multiple documents need to be updated if the information changes but that all related data can be fetched with a single query.
11. What is Cardinality?
Answer:
Cardinality is how many references a collection has to another collection. Common relationships are one-to-one, one-to-many, or many-to-many.
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12. When not to use MongoDB?
Answer:
MongoDB does not support transactions, so systems that require transactions should use another data store. There are a couple of ways to hack in simple transaction-like semantics, particularly on a single document, but there is no database enforcement
13. What is replication in MongoDB?
Answer:
Replication is a way of keeping identical copies of your data on multiple servers and is recommended for all production deployments. Replication keeps your application running and your data safe, even if something happens to one or more of your servers. With MongoDB, you set up replication by creating a replica set. A replica set is a group of servers with one primary, the server taking client requests, and multiple secondary’s, servers that keep copies of the primary’s data. If the primary crashes, the secondary’s can elect a new primary from amongst themselves.
14. What is the command used to set replication in MongoDB?
Answer:
replicaSet = new ReplSetTest({"nodes" : 3})
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15.when Rollback fails in MongoDB?
Answer:
MongoDB decides that the rollback is too large to undertake. Rollback can fail if there are more than 300 MB of data or about 30 minutes of operations to roll back. In these cases, you must re-sync the node that is stuck in rollback.
16. What is Sharding in MongoDB?
Answer:
Sharding refers to the process of splitting data up across machines the term partitioning is also sometimes used to describe this concept. By putting a subset of data on each machine, it becomes possible to store more data and handle more load without requiring larger or more powerful machines, just a larger quantity of less-powerful machines.
17. What is Manual Sharding?
Answer:
Manual sharding can be done with almost any database software. Manual sharding is when an application maintains connections to several different database servers, each of which is completely independent. The application manages to store different data on different servers and querying against the appropriate server to get data back. This approach can work well but becomes difficult to maintain when adding or removing nodes from the cluster or in the face of changing data distributions or load patterns.
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