Oracle Point, Oracle Life.

Today, I spent 30 minutes to re-read the Oracle official doc “Redo Logs and Recovery” and got my knowledge newly refreshed about this key concept with Oracle. Most importantly, I got the chance to know deeper about that.

I’m writing several points below for my own reference.

Point 1: Data in Redo Log Buffer was written to redo log file even though it’s not committed, at some circumstances.

Point 2: A checkpoint necessarily happens while redo log switch to performs the following three operations:

1. Every dirty block in the buffer cache is written to the data files. That is, it synchronizes the data blocks in the buffer cache with the datafiles on disk.
   It’s the DBWR that writes all modified database blocks back to the datafiles.
2. The latest SCN is written (updated) into the datafile header.
3. The latest SCN is also written to the control files.

Point 3: Beginning with 9i, new mechanism is implemented to improve performance while recovery.

In summary, that’s a real good official article to learn deeper internals of Redo Log and Recovery.

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