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Connor McDonald

Thanks for the question, Nitin.

Asked: March 31, 2021 - 5:30 am UTC

Last updated: April 07, 2021 - 4:17 am UTC

Version: 12.1

Viewed 100+ times

You Asked

Hello Tom,

I just wanted to know use of Checkpoint & scn.

I know the basic definition but want to know in what are all the situation it occurs & how it will be use in case of Oracle recovery.

Can you please explain me with an example.

Thanks,
Nitin

and we said...

Think of yourself sitting wherever you are right now. How did you end up there?

One way you could work it out would be to go right back to your birth...

- Born
- Picked up and put in a crib
- Crib rocked
- Then you were bathed and fed
- Put back in crib
...
...
...
- Came home from school
- Ate dinner
- went and played some sport
...
...
...
- Went to the Office
- Came home
- Sat down at table
- AND HERE WE ARE!

If you have a record of *every time* you moved since birth, you could play that forward and work out where you are right now.

But thats....slow :-) A better way would be to keep a note from time to time of where you are so you can work from there. For example, with the above:

- Born
- Picked up and put in a crib
- Crib rocked
- Then you were bathed and fed
- Put back in crib
...
...
...
- Came home from school
- Ate dinner
- went and played some sport
...
...
...
- Went to the Office
***OK - LETS REMEMBER THAT WE WERE AT THE OFFICE AT THIS POINT IN TIME***
- Came home
- Sat down at table
- AND HERE WE ARE!

Now when someone asks me how I got here, I go:

- OK, I know I was at the office yesterday. So I'll start from there
- Came home
- Sat down at table
- AND HERE WE ARE!


Much quick and more efficient.

Every change you did since birth we could give a number to. Birth = change 1, crib = change 2, etc.....That is your system change number and you redo logs, ie, every change you ever did.

Taking occasional reminders of where you are so that you don't have to go back to birth every time to work out .... That is your datafiles. A point time in moment of where you're up to. The checkpoint is the information on the datafile saying "Hey, these are files are up to change 2624", so you can start from there and work forward.

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