Oracle Learning Note-oracle Architecture and status (Nomount, Mount, and open)

Introduction to Oracle Architecture

Let's take a brief look at the Oracle database architecture for an in-depth understanding of Oracle server primarily by instance (instance) and database ( Database) . instance ( instance ) consists of a shared memory (SGA) and a background process system , the database ) is a series of physical files stored on disk.

The

SGA is primarily made up of Share pool (Shared pool, also library cache and data Dictionary cache, which temporarily stores recently executed statement code, etc.). The latter temporarily stores data locations, table definitions, user permissions, and so on), Database buffer Cache (data buffers, temporary storage of read blocks), Redo Log buffer (Redo the log buffer, temporarily store database modification operations), Large pool (large pool, share share pool portion of work for use by shared server processes, such as backup recovery, large I/O operations, parallel queries, etc.), and Java Pool (Java pools, parsing Java statements).

The

background process is the channel through which the database interacts with the operating system, the naming of the background process is determined by ORACLE_SID, and Oracle is looking for a parameter file to launch the instance based on Oracle_sid. is set by the Oracle database to maintain optimal performance and coordinate multi-user requests, primarily DBWR (writes database Buffer cache data to Data Files), LGWR (writes redo log buffer data to redo log files), CKPT (Reconcile data files, control files, and redo logs to Number is the SCN written to the control file and data file header, prompting DBWR, lgwr execution), Smon (System monitor,3 Role: Instance recovery instance failure data recovery, Merge idle fragmentation space, reclaim temporary segments), Pmon (process transactions when a user routine terminates unexpectedly, such as fallback transactions, release locks, and other resources), ARCH (Redo Log Files are written to archive Log Files), CJQ0 (Job queue Coordinator), RVWR (recover writer, Provides logging for flashback database) processes.

Databases (Database ) refers to a set of physical files stored on disk, such as data Files , which are used to store data, control files , storage data files, redo log files, Archive log file locations and information required to maintain database integrity) and redo log files (Redo log file, which stores all operational records of modified data for recovery after a failure), these three are the files required to start the database, and the parameter files (Parameter file, set the startup of the memory daemon process, etc.), archive log file (archived log files, archive the contents of a full redo log file) and a password file (Password. Verify user name password), these three are non-mandatory files.

Oracle Boot Status

Oracle startup is divided into 3 processes Nomount, mount, and open, and the three processes specifically perform the following tasks:

• Nomount Status: SGA and background process has started
• Mount Status: The control file is read through the parameter, the backup and restore operation with SYSDBA permission can make some data, other users can't access
• Open state; normal access for other users

nomount StatusCreate a DB instance first read the database parameter file from SPFile or pfile, then assign the SGA and create a background process. The equivalent of the production line and the workers are in place, but no production started, no products on the production line. The Mount State establishes the relationship between the database and the instance. First, according to the Control_file parameter in the initialization parameters file, find the corresponding control file and then open them, in the control file contains the database data files and redo log file information. This time the database is not open, still in the shutdown state, this time ordinary users can not connect to the database, only the database administrator to do some backup recovery work.  Open state

Open the database.

By controlling the file information to find the online data file and the redo log file, if there are no more than two files, the database will be an error. If the two files are broken and the database cannot be opened, the data files can be restored and then opened after the SYSDBA permission has been entered into the Mount Mount state.

Reference:

Oracle database startup process and status explained (Nomount, Mount and Open)

Four states initiated by Oracle

Oracle Learning Note-oracle Architecture and status (Nomount, Mount, and open)