What application scenarios consider using MONGDB?

MySQL and Redis are very good and skilled, what scenario should I discard these tools and instead consider using MONGO to store data?

Other than that:
Currently in the exploration of the storage article type of data, the style of the article content needs to be saved, and does not destroy the retrieval tool on the content of the retrieval ability, performance has to go, I need a good solution, for the characteristics of the database and comparison I will certainly be in advance to check the information, so the answer is not simple comparison database features, My practical problems may be biased towards actual combat and experience.

Do a daily order million app backstage, with MySQL and Redis, for general problems MySQL and Redis can support, what reason or scene will force me or recommend me to use MONGO, MONGO flexible data type storage, I currently only think of log storage with MONGO better. Article Class of the site I novice development, need experience guide, first thank you

Reply content:

MySQL and Redis are very good and skilled, what scenario should I discard these tools and instead consider using MONGO to store data?

Other than that:
Currently in the exploration of the storage article type of data, the style of the article content needs to be saved, and does not destroy the retrieval tool on the content of the retrieval ability, performance has to go, I need a good solution, for the characteristics of the database and comparison I will certainly be in advance to check the information, so the answer is not simple comparison database features, My practical problems may be biased towards actual combat and experience.

Do a daily order million app backstage, with MySQL and Redis, for general problems MySQL and Redis can support, what reason or scene will force me or recommend me to use MONGO, MONGO flexible data type storage, I currently only think of log storage with MONGO better. Article Class of the site I novice development, need experience guide, first thank you

To list out the appropriate usage is ...

We think in turn, what scenario is not suitable for mangodb?

We have a user personal center:
A user can have a lot of friends, friends can have a lot of messages, messages can have a lot of replies, messages can have a lot of people praise

Using MongoDB to model, is a large JSON, inside we have a user, and then the user has a friend array, message array, reply to an array, like the user array, these arrays are full of information, the query time to all get to!

However, a problem has been brought
Because friends in the array of friends information is actually user information, so the storage of complete information resulting in data redundancy, this problem is also good solution, that is, in the array to store the ID, and then according to the ID to the corresponding data source to check the data,

However, MongoDB does not have a join operation, so it is important to do the related work manually in the code layer.

In this way, MongoDB is not suitable for storing data that has relationships, relationships, relationships, and the like.

Why you should not use MongoDB
Why you should never use MongoDB

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