Re: Concepts question about Redo Log Files

Paul <bfekrat_at_erols.com> wrote:
>Could someone please explain to me the reason we must have redo log
>files? That is, why can't we just write committed transactions directly
>to the data files?
>
>I understand the importance of multiplexing the redo log files for
>backup and recovery issues. I also can see how a small, sequential redo
>log file might be written to by Oracle, slightly faster than the actual
>data file. But I just don't see why, in theory, we couldn't do away
>with the redo log files. Someone please help explain this to me as I
>will not be able to sleep until I fully understand WHY!!!!!!
>
>Paul

Hi there,

When a record is updated, Oracle changes only the data buffers (dirties the buffer) in the SGA. It does not change the datafiles. It is upto the DBWR to pickup the dirty buffers and write to the data files (or) if a check point process is enabled, it signals the DBWR to pickup all the dirty buffers and make changes permanent.

This setup makes DBWR efficient (it is stated in Oracle manual). Since there is a timelag between this exercise, redo log files are generated. According to some Oracle books, is is mentioned that DBWR acts more efficiently in this pattern. I am not sure what is % increase in performance by adopting this strategy.

If you happen to get some more info, please forward it to me.

Regards

N.Prabhakar Received on Sat Jan 04 1997 - 00:00:00 CST