When LGWR process writes to Redo Log file and What is Log Switch

LGWR background process will start to write dirty buffers from Log Buffer to one of the group of Online Redo Log files under following circumstances:

1. When the user commits transaction;

2. When Log buffer fills of 1/3;

3. When dirty buffers exceeds 1M in log buffer;

4. Before DBWn writes dirty buffer into datafile.



What is Log switch and what happens when it occurs?

When one of the Redo Log group is full, LGWR jumps to following Log group to write dirty buffers. This action called Log Switch. Checkpoint operation will occur and header of Datafile, control files will be updated by CKPT with SCN and Checkpoint numbers. DBWn also writes dirty buffers from DB Buffer cache to data file.