Top 101 MongoDB Interview Questions 2019

MongoDB 

MongoDB is an open source document database4 and leading NoSQL database. It’s a powerful, FREE & highly scalable NoSQL database. Its very popular choice of a highly scalable database and currently being used as the backend data store of many well-known organizations like Google, Facebook, Twitter, Forbes, IBM. MongoDB is widely used across various web application. Its most used by MEAN stack developers as the data store.

So Let’s dive deep. It’s basically a document-based data store (stores data) in an unstructured format. unstructured data is also known as “schema-less” data. This the reason MongoDB provides a fast and scalable data storage service which makes it a most popular choice in performance critical application.

Now you might have thought about how to learn? Okay, the best way to learn MongoDB is to develop a web application that uses MongoDB as the database. MongoDB can accommodate large documents of up to 16 MB. But keeping mind accommodating large file is not good it’s highly recommended to keep individual documents to small kilobytes in size. Here is the 6 rule of thumb for MongoDB schema design

MongoDB Interview Questions – 101 Questions

1. Explain what is MongoDB?
2. What is “Namespace” in MongoDB?
3. What is sharding in MongoDB?
4. How can you see the connection used by Mongos?
5. Explain what is a replica set?
6. How replication works in MongoDB?
7. While creating Schema in MongoDB what are the points need to be taken in consideration?
8. What is the syntax to create a collection and to drop a collection in MongoDB?
9. Explain what is the role of profiler in MongoDB?
10. Explain can you move old files in the moveChunk directory?
11. To do safe backups what is the feature in MongoDB that you can use?
12. Mention what is Objecld composed of?
13. Mention what is the command syntax for inserting a document?
14. Mention how you can inspect the source code of a function?
15. What is the command syntax that tells you whether you are on the master server or not? And how many master does MongoDB allow?
16. Mention the command syntax that is used to view Mongo is using the link?
17. Explain what are indexes in MongoDB?
18. Mention what is the basic syntax to use index in MongoDB?
19. Explain what is GridFS in MongoDB?
20. What are the best features of MongoDB?
21. When using replication, can some members use journaling and others not?
22. Can journaling feature be used to perform safe hot backups?
23. What is 32-bit nuances?
24. Will there be journal replay programs in case of incomplete entries (if there is a failure in the middle of one)?
25. What is the role of profiler in MongoDB?
26. What is a ‘namespace’?
27. When an object attribute is removed, is it deleted from the store?
28. Are null values allowed?
29. Does an update fsync to disk immediately?
30. How do I do transactions/locking?
31. Why are data files so large?
32. How long does replica set failover take?
33. What’s a Master or Primary?
34. What’s a Secondary or Slave?
35. Is it required to call ‘getLastError’ to make a write durable?
36. Should you start out with Sharded or with a Non-Sharded MongoDB environment?
37. How does Sharding work with replication?
38. When will data be on more than one Shard?
39. What happens when a document is updated on a chunk that is being migrated?
40. What happens when a Shard is down or slow when querying?
41. Can the old files in the ‘moveChunk’ directory be removed?
42. How do you see the connections used by Mongos?
43. If a ‘moveChunk’ fails, is it necessary to cleanup the partially moved docs?
44. What are the disadvantages of MongoDB?
45. What are NoSQL databases? What are the different types of NoSQL databases?
46. What kind of NoSQL database MongoDB is?
47. Which are the most important features of MongoDB?
48. What is a Namespace in MongoDB?
49. Which all languages can be used with MongoDB?
50. Compare SQL databases and MongoDB at a high level.
51. How is MongoDB better than other SQL databases?
52. Compare MongoDB and CouchDB at high level.
53. Does MongoDB support foreign key constraints?
54. Does MongoDB support ACID transaction management and locking functionalities?
55. How can you achieve primary key – foreign key relationships in MongoDB?
56. Does MongoDB need a lot of RAM?
57. Does MongoDB pushes the writes to disk immediately or lazily?
58. Explain the structure of ObjectID in MongoDB.
59. MongoDB uses BSON to represent document structures. True or False?
60. If you remove a document from database, does MongoDB remove it from disk?
61. Mention the command to insert a document in a database called school and collection called persons.
62. What are Indexes in MongoDB?
63. How many indexes does MongoDB create by default for a new collection?
64. Can you create an index on an array field in MongoDB? If yes, what happens in this case?
65. What is a covered query in MongoDB?
66. Why is a covered query important?
67. Does MongoDB provide a facility to do text searches? How?
68. What happens if an index does not fit into RAM?
69. Mention the command to list all the indexes on a particular collection.
70. At what interval does MongoDB write updates to the disk?
71. How can you achieve transaction and locking in MongoDB?
72. What is Aggregation in MongoDB?
73. What is Sharding in MongoDB? Explain.
74. What is Replication in MongoDB? Explain.
75. What are Primary and Secondary Replica sets?
76. By default, MongoDB writes and reads data from both primary and secondary replica sets. True or False.
77. Why are MongoDB data files large in size?
78. When should we embed one document within another in MongoDB?
79. Why MongoDB is not preferred over a 32-bit system?
80. What is a Storage Engine in MongoDB
81. Which are the two storage engines used by MongoDB?
82. What is the role of a profiler in MongoDB? Where does the writes all the data?
83. How does Journaling work in MongoDB?
84. Mention the command to check whether you are on the master server or not.
85. Can you configure the cache size for MMAPv1? How?
86. Can you configure the cache size for WiredTiger? How?
87. How does MongoDB provide concurrency?
88. How can you isolate your cursors from intervening with the write operations?
89. Can one MongoDB operation lock more than one databases? If yes, how?
90. How can concurrency affect replica sets primary?
91. What is GridFS?
92. Can you run multiple Javascript operations in a single mongod instance?
93. Which command can be used to provide various information on the query plans used by a MongoDB query?
94. What is BSON in MongoDB?
95. What is _id Field in MongoDB?
96. How do you create or select a database in MongoDB?
97. What is collection in MongoDB?
98. What is writeConcern?
99. What is upsert?
100. Explain some of the Evaluation Query Operators.
101. What is Storage Engine? What are all the Storage Engines available in MongoDB?