SQL Server: storage engine (I): system default database

The system includes the following databases by default:
1. Master: It is composed of some system tables which track the system installation as a whole and other databases subsequently created. Although no database has a set of system directories that contain object information, some system directories in the master database can maintain disk space, file allocation and usage, and system-level configuration information, the endpoint of the Logon account.
2. Model: A template database. Whenever we create a new database, SQL Server copies the model database as the basis for the new database. If you want each new database to contain certain objects or permissions during creation, modify the model database.
3. tempdb: Used as a workspace. Every SQL serverc restart will be rebuilt instead of restored. The user displays the created temporary table and the worksheet that generates intermediate results during SQL Server Query Processing and sorting, and maintains the versions used for Snapshot isolation level and some other operations, the database is used to fill in the static cursor and the key value of the key set cursor. therefore, it has a profound impact on SQL server performance.
4. mssqlsystemresource: it is a hidden database, also known as a resource database. Executable system objects, such as system stored procedures and functions, are stored here. Microsoft created it to facilitate updates and upgrades.
5. MSDB: the MSDB database used by the sqlserver proxy service. It executes scheduled activities such as backup and replication tasks. Services broker also uses MSDB. It provides queues and reliable message transmission for SQL Server.