Hi I want to know how MongoDB save documents, for example, this create a single one file for each document?
No it does not. See https://docs.mongodb.com/manual/core/wiredtiger/ for more information.
Welcome to the MongoDB Community Forums @Jean_N_A !
In addition to the general storage engine reference that @steevej provided, you may find some of the following details helpful:
The server-side representation of a document uses BSON data types. BSON is binary JSON-like serialisation format that adds additional data types such as numeric (32-bit integer, 64-bit integer, 128-bit Decimal), Date, and ObjectId.
MongoDB drivers handle server communication and serialisation, so you usually end up working with native objects in your chosen development language rather than directly writing BSON.
Documents are stored on disk using block compression to reduce storage usage. Documents are automatically uncompressed in memory when retrieved by the MongoDB server.
Each collection & index is stored in a separate file within the
storage.dbPathfor your deployment. The
dbPathalso includes other essential metadata files for your deployment, so a valid backup requires the full contents of your
dbPathor a copy of your data via a supported MongoDB Backup Method.