MongoDB interview questions

1. What is a NoSQL database? What is the difference between NoSQL and RDBMS? Under what circumstances do I use and do not use NoSQL databases?

NoSQL is a non-relational database, NoSQL = Not Only SQL.

Relational databases use structured data, while NoSQL uses key-value pairs to store data.

When processing unstructured/semi-structured big data, when scaling horizontally, NoSQL databases are preferred when dealing with dynamically increasing data items at any time.

Relational databases should be given priority when considering issues such as database maturity, support, analysis and business intelligence, management and professionalism.

2. What are non-relational databases?

Membase, MongoDB, and Hypertable

3. What is the most basic difference between MySQL and MongoDB?

The difference between a relational database and a non-relational database is that the data storage structure is different.

4. What are the characteristics of MongoDB?

(1) Documentation oriented (2) High Performance (3) high availability (4) Easy Scalability (5) rich query languages

5. Does MongoDB support stored procedures? How can I use it if it is supported?

MongoDB supports the stored procedure, which is written in javascript and saved in the db. system. js table.

6. How to understand the GridFS mechanism in MongoDB and why does MongoDB use GridFS to store files?

GridFS is a file specification that stores large files in MongoDB. GridFS can be used to separate large files into multiple small files for storage, so that we can effectively save large files and solve the limitation of BSON objects.

7. Why is MongoDB's data file large?

MongoDB uses pre-allocated space to prevent file fragments.

8. What will happen when updating the document on a Chunk being migrated?

The update operation will immediately occur on the old Chunk, and the change will be copied to the new shard before the ownership transfer.

9. MongoDB creates an index on A: {B, C}. Will indexes be used for queries A: {B, C} And A: {C, B?

No, the index will only be used on A: {B, C.

10. What if a Shard is stopped or slow?

If a shard is stopped, an error is returned if the "Partial" option is set for the query. If the response of a shard is slow, MongoDB will wait for its response.