MongoDB's system

The logical structure of MongoDB

Mainly consists of three parts: Document, Collection (collection) and database.

MongoDB Document: The basic unit of data in MongoDB, equivalent to a row of records in a relational database, each document has a special key "_id", which is unique within the collection to which the document belongs.

Collection (collection): equivalent to the concept of a table in a relational database

A hierarchy of documents, collections (collection), databases (database) such as:

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Document corresponds to rows in relational data (row)

Tables (table) in the corresponding relational data set (collection)

Database (database) in relational data

MongoDB Data Directory stores all MongoDB data files

[[Email protected] data]$ ll Total dosage  1212436drwxr-xr-x. 2 mongo dbmon          69 10 month  28 17:15 diagnostic.datadrwxr-xr-x.  2 mongo dbmon         27 10 Month  28  15:25 JOURNAL-RW-------.  1 mongo dbmon   67108864 10 Month  28  15:25 LOCAL.0-RW-------.  1 mongo dbmon 1073741824 10 Month  28 17:15  LOCAL.1-RW-------.  1 mongo dbmon   16777216 10 Month  28 17:14  Local.ns-rw-r--r--.  1 mongo dbmon          6  10 Moon  28 15:17 mongod.lock-rw-r--r--.  1 mongo dbmon          69 10 month  28 15:17 STORAGE.BSON-RW-------.  1 mongo  dbmon   67108864 10 Moon  28 17:00 SYKDB.0-RW-------.  1 mongo dbmon    16777216 10 Month  28 17:00 sykdb.nsdrwxr-xr-x. 2 mongo dbmon           6 10 Month  28 15:54 _tmp

Inside MongoDB, each database contains an. ns file and some data files, such as: LOCAL.NS,LOCAL.0,LOCAL.1, and the number of files increases as the volume of data grows.

Each table corresponds to a namespace, and each index has a corresponding namespace. The metadata for these namespaces is placed in the *.ns file.

MongoDB has a pre-allocated space mechanism, and pre-allocated files are populated with 0, so MongoDB always keeps extra space and free data files. Each time a new file is generated for a data file, it will be twice times the size of the previous data file. Like my local.0 is 67108864,LOCAL.1 or 1073741824.

Reference: MongoDB Series-Architecture

This article is from the "just out of the shell of the Birds" blog, please be sure to keep this source http://qhd2004.blog.51cto.com/629417/1866883

MongoDB's system