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.