以下摘自Oracle log files : An introduction

Online redo Oracle log files are filled with redo records. A redo record, also called a redo entry, is made up of a group of change vectors, each of which is a description of a change made to a single block in the database.

Redo日志文件由redo record组成,每个redo record(又称作redo entry)又由一组change vector构成。

The online redo log file that Log Writer (LGWR) is actively writing to is called the current online redo log file. Online redo Oracle log files that are required for instance recovery are called active online redo log files. Online redo log files that are not required for instance recovery are called inactive.


SQL> select group#,members,bytes/1024/1024,status from v$log;

---------- ---------- --------------- ----------------
         1          1             100 INACTIVE
         2          1             100 ACTIVE
         3          1             100 INACTIVE
         4          1             300 CURRENT




以下摘自Oracle 12c For Dummies

The checkpoint process(CKPT) is responsible for initiating check points. A check point is when the system periodically dumps all the dirty buffers to disk. Most commonly, this occurs when the database receives a shutdown command. It also updates the data file headers and the control files with the check point information so the SMON know where to start recovery in the event of a system crash.