Online redo log files are very important for the functionality of the database.
Every change initially will be recorded into online redo log file.
Minimal information will be recorded into online redo log file if the tablespace is created with "nologging".
Prior to 10g, the minimum size of the online redo log file is 64K whereas from 10g, it is 4MB.
If we create a database with DBCA, oracle creates online redo log files of sizes 50MB.
In the industry, generally the sizes of online redo log files will be in MB's.
Without redo log files, database will not function.
Since redo log files are very important, recommanded to mirror them to avoid single point of failures(keep mirrored copied in ta separate file system).
Identical copies of online redo log files within a group are called "members".
Members within a group contains the same data and contains the same log sequence number.
Log Writer writes the data into the online redo log files in cyclic manner.
Log Writer writes the data into online redo log fies under the following circumstances :
1.If 1/3 of redo buffer cache is filled
2.IF the data reaches 1 MB
3.If the user commits
4.For every 3 seconds
5.Before DBWR writes to respective datafiles
