Bookish query Regarding Redo Log

From: Arijit Chatterjee <arijitchatterjee123_at_yahoo.co.in>
Date: 4 Nov 2004 20:55:24 -0800
Message-ID: <ea01504d.0411042055.291dcd47@posting.google.com>

Respected Faculties,
Again one more doubt has arised in my mind and I need some guidance from you people.I am explaining the doubt..

I got these lines from Oracle Documentation

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LGWR writes to online redo log files in a circular fashion. When the current online redo log file fills, LGWR begins writing to the next available online redo log file. When the last available online redo log file is filled, LGWR returns to the first online redo log file and writes to it, starting the cycle again. Figure 7-1 illustrates the circular writing of the online redo log file. The numbers next to each line indicate the sequence in which LGWR writes to each online redo log file.....

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Sorry I couldn't draw the picture(Figure 7-1)

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Now I have a question on this.

Scenario

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Instance X useing thread 1, which contains two groups of online redo log files (groups 1, 2). Thread 1 is multiplexed, that is, each group has two copies (members) of the redo log files.

So as per above definition when group 1 is filled up then LGWR start to write on group 2.But after filling up Group 2 it again swiches to Group 1.

Now I have a doubt on this point..
1.Does it over write the existing contain of Redo log   files.
2.If yes then how to identify that LGWR is now end of   present Redo Log.If I need to archive the next Redo   Log file do that..

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I tried my level best to explain the doubt.If you have some problem to understand the query please let me know.

Regards
Arijit Chatterjee Received on Thu Nov 04 2004 - 22:55:24 CST