My Oracle Learning Note (iii)-----architecture

1. Physical structure (composed of control files, data files, redo log files, parameter files, archive files, password files)
Control files: Contains necessary information to maintain and verify database integrity, for example, control files are used to identify data files and redo log files, and a database requires at least one control file
Data files: Files that store data
Redo log files: Contains a record of the changes made to the database so that data recovery can be enabled in the event of a failure. A database requires at least two redo log files
Parameter file: Defines the attributes of an Oracle routine, for example, it contains parameters that adjust the size of some memory structures in the SGA
Archive: is an offline copy of the redo log files that may be necessary to recover from media failure.
Password files: Authenticate which users have permission to start and close Oracle routines

2. Logical Structure (table space, segment, area, block)
Tablespace: Is the basic logical structure in a database, a collection of data files.
Segment: Is the space that the object occupies in the database
Zone: is a large storage space reserved for data once
Block: Oracle's most basic storage unit, specifying when the database is built

3. Memory allocation (SGA and PGA)
SGA: Is the memory area used to store database information that is shared by the database process. It contains data and control information for the Oracle server, which is allocated in the actual memory of the computer where the Oracle server resides, if the actual memory is not enough to be written in virtual memory.
PGA: Contains data and control information for a single server process or a single background process, which is the same as the SGA shared by several processes the PGA is a zone that is used only by one process, and the PGA is allocated when the process is created to recycle when the process is terminated

4. Background process (data write process, log write process, System Monitor, process monitoring, checkpoint process, archive process, service process, user process)
Data write process: Responsible for writing changed data from the database buffer cache to the data file
Log write Process: Writes changes in the redo log buffer to the online redo log file
System monitoring: Check database consistency If necessary also initiates recovery of the database when the database is opened
Process monitoring: Responsible for cleaning up resources in the case of an Oracle process failure
Checkpoint process: Updates the database state information in the control files and data files whenever changes in the buffer cache are permanently logged in the database.
Archive process: Back up or archive a full log group at each log switch
Service process: User process Service.
User process: On the client side, is responsible for passing the user's SQL statement to the service process and taking back the query data from the server segment.

5. Oracle Routines: Oracle routines consist of the SGA memory structure and the background process used to manage the database. A routine can only open and use one database at a time.

6. SCN (System change number): The number of systems changes, a sequence of internal maintenance by the system. When the system needs to be updated automatically increases, he is the system to maintain data consistency and sequential recovery of important signs.

My Oracle Learning Notes (iii)-----architecture