Oracle checkpoint 说明

 

 

一. Oracle Checkpoint 说明

 1.1  Checkpoint

（1）A synchronization event at aspecific point in time

（2）Causes some or all dirty blockimages to be written to the database thereby guaranteeing that blocks dirtiedprior to that point in time get written

（3）Brings administration up to date

（4）Several types of checkpoint exist

 

RedoLog Checkpoint 和 SCN关系

http://blog.csdn.net/tianlesoftware/article/details/5251916

 

Oracle 实例恢复时 前滚（roll forward） 后滚（rollback） 问题

http://blog.csdn.net/tianlesoftware/article/details/6286330

 

1.2  the point of Oracle Checkpoints

       The point of Oracle checkpoints is to synchronize all datafiles, some datafiles orsome objects to a point in time for consistency, performance and recoverabilitypurposes.

  

1.3 Buffer Cache

       checkpoint与Buffer Cache 的关系很大，有关Buffer cache，之前整理的相关文章如下：

Oracle Buffer Cache 原理

http://blog.csdn.net/tianlesoftware/article/details/6573438

 

Oracle Buffer Cache 中的Recycle Pool 说明

http://blog.csdn.net/tianlesoftware/article/details/6584110

 

Oracle Buffer Cache 中 KeepPool 说明

http://blog.csdn.net/tianlesoftware/article/details/6581159

 

1.3.1 buffer cache 组成

The buffer cache component structures are:

（1）Buffers

       Eachbuffer may hold an image of one data block at any one time

（2）Buffer headers

       =>Storemetadata about contents of the buffers

       =>Actas cache management structures

（3）Buffer pools

       Collectionof buffers used for the same purpose and managed accordingly

（4）Working set

       =>Allor part of a buffer pool

       =>Assigned to a DBWn process

 

1.3.2 Buffer Management

（1） Cached buffers managed by doublylinked lists:

（2） REPL

              =>Bufferscontaining block images being used

（3） REPL-AUX

             =>Buffersready to be used for I/O or CR build

              关于CR 参考：

              CR (consistent read) blockscreate 说明

              http://blog.csdn.net/tianlesoftware/article/details/6529401

（4） WRITE and CKPT-Q

             =>DirtyBuffers requiring I/O

（5） WRITE-AUX

             =>DirtyBuffers with I/O in progress

（6） Touch count is used to decide theinitial insertion location in the REPL chain

（7） AUX lists avoid wasteful scanning

 

1.3.3 Redo and the Buffer Cache

（1） Block modification dirties thebuffer containing the block image and generates redo

（2） A buffer becomes dirty at aparticular RBA which is a point in the redo stream

       关于RBA,参考我的blog：

       Oracle RBA(Redo Byte Address) 说明

       http://blog.csdn.net/tianlesoftware/article/details/6700080

（3） Redo written by LGWR makes thecorresponding part of the redo log file “active”

（4） Dirty block images written by DBWnmakes the corresponding part of the redo log file “inactive”

（5） Redo is always written priorto the corresponding block images

（6） Size of active redo in the logfile influences instance and crash recovery time

（7） Trade-off between performance andrecovery time

 

1.3.4 Buffer Cache I/O

（1）Servers look for an availablebuffer on REPL-AUX then read a data block into selected buffer

      

Link URL: http://blog.csdn.net/tianlesoftware/article/details/6700085