oracle 体系架构 （绝对原创） （一）

This I will intruduce Instance and Media recovery structure:
 
  After completing this lesson, you should be able to do the following:
 
  1: Describle the Oracle process, memory structures, and file rekating to recovery.
  2: Identify the importance of checkpoints, redo log files, and archived log files.
  3: Describe ways to tune instance recovery.
 

Step1:
  Memory:
  Type:
  1: Data buffer cache:
    Menory area used to store blocks read from data files.
    Data is read into the blocks by server process and written out by DBWn asynchronously.
   
  2: Log buffer:
     Memory containing before and after image copies of changed data to be written to redo logs.
    
  3: Large pool:
    An optional area in the SGA that provides large memroy allocations for backup and restore operations.
    I/O server processes, and session memory for the shared server and ORACLE XA.
   
  4: Shared pool:
     Stores parsed version of SQL statements, PL/SQL procedures, and data dictionary information.
    
  5: Jave pool:
     Used in server memory for all session-specific Jave Code and data within the java virtual mechine.
    
Step2 Backgroud Process:
 
  1: Database write (DBWn):
    writes dirty buffers from the data buffer cache to the data files, This activity is asynchronous.
   
    Notice:
    If you are using the linux OS , the packet: "aio" is nessary to asynchronous packet:
    rpm -qa | grep aio
    libaio-devel-0.3.105-2
    libaio-0.3.105-2
   
  2: Log write (LGWR)
    write data from redo log buffer to the redo log files.
   
  3: System Monotor (SMON):
     Perform automatic instance recovery, Recoverys sapce in temporary segments when
     they are no longer in use. Merges contiguous areas of free space depending on parameters that
     are set.
    
  4: Process Monitor (PMON):
     Cleans up connection/server process dedicate to an abnormally terminated user process.
     performs rollback and releas the resources held by failed process.
    
  5: Checkpoint (CKPT):
     synchronize the headers of the data files and control files with the current redo log and
     checkpoint number.
    
  6: Archiver (ARCn):
     A process that automatically copies redo logs that have been marked for archiving.
    
Step3:
   Database Files:
   An oracle database consists of the following physical files:
   1: datafiles:
     PHysical storage of data, At least one file is needed per database. This file stores system tablespace.
    
   2: Redo logs:
     Contain before and after image copies changed data, for revocery purpose, at least, two files are required.
    
   3: Control files:
     record the status of the database, physical structure, and RMAN meta data.
    
   4: Archive logs (optional):
     physical copies of the online redo log files, created when the database is set in  archivedlog mode.
     It is used in recovery.