before image vs checkpoint for recovery?

I read recently that if a before-image was made before an interruption in database processing, you use the before-image dump & simply begin processing again from just before the last transaction. Any checkpoints are irrelevant.

What I don't understand is, why are checkpoints irrelevant when you did a before image dump? Why not begin from the last checkpoint? Probably part of my problem is understanding the difference between the before image dump and a checkpoint. I know that the checkpoint is a db even that suspends processing & writes data to the disk. It represents a moment in time when everything is OK in the db. That sounds a lot like a before image dump :) Maybe the checkpoint is further back in time (?)

Thanks for any clarification
Jason Shohet Received on Mon May 30 2005 - 12:40:15 CDT