1.先來看下外國網站上的資料怎么說
- Nomount – The database instance has been started (processes and memory structures have been allocated, but control file is not yet accessed). 數據庫實例已經開始（進程和內存已經分配，但是控制文件還沒有啟動）
- Mount – Instance has accessed the control file, but has not yet validated its entry or accessed the datafiles. 實例已經開啟控制文件，但是還沒有開啟數據文件
- Open – Instance has validated the entries in the control files and is accessing the datafiles – it is now open for business. 開啟數據文件
2.nomount階段
- read the spfileSID.ora initSID.ora
- Allocating the SGA
- Starting the background processes
- Opening the alertSID.log file and the trace files
3.mount階段
- Associating a database with a previously started instance
- Locating and opening the control files specified in the parameter file
- Reading the control files to obtain the names and status of the data files and online redo log files.However,no checks are performed to verify the existence of the data files and online redo log files at this time.
4.open狀態
- opening the online datafiles
- opening the online redologs