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mongodbembeddingdenormalization
Jamie
Jamie

Reputation: 3051

What does denormalizing mean?

While reading the article http://blog.mongodb.org/post/88473035333/6-rules-of-thumb-for-mongodb-schema-design-part-3 chapter: "Rules of Thumb: Your Guide Through the Rainbow" i came across the words: embedding and denormalizing.

One: favor embedding unless there is a compelling reason not to

Five: Consider the write/read ratio when denormalizing. A field that will mostly be read and only seldom updated is a good candidate for denormalization: if you denormalize a field that is updated frequently then the extra work of finding and updating all the instances is likely to overwhelm the savings that you get from denormalizing.

I know embedding is nesting documents, instead of writing seperate tables/collections.

But i have no clue what denormalizing means.

Upvotes: 0

Views: 436

Answers (1)

Simulant
Simulant

Reputation: 20102

Denormalization is the opposite of normalization, a good practice to design relational databases like MySQL, where you split up one logical dataset into separated tables to reduce redundancy.

Because MongoDB does not support joins of tables you prefere to duplicate an attribute into two collections if the attribute is read often and less updated.

E.G.: You want to save data about a person and want to save the gender of the Person:

In a SQL database you would create a table person and a table gender, store a foreign key of the genders ID in the person table and perform a join to get the full information. This way "male" and "female" only exists once as a value.

In MongoDB you would save the gender in every Person so the value "male" and "female" can exist multiple times but the lookup is faster because the data is tightly coupled in one object of a collection.

Upvotes: 2

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