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RMAN ckpn SCN and cumulative differential backup
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Message Score Author Date
Hi all I need to understand several concepts i...... sze jie koh Aug 06, 2020, 15:25
Hi Noob, 1) Not sure, rman internals; you can g...... Philip Wisse Aug 10, 2020, 17:46
#3 Adding a reference: https://docs.oracle.com/d...... Philip Wisse Aug 13, 2020, 15:42
Hi Philip 1) so do you think i should not pay a...... sze jie koh Aug 14, 2020, 07:03
Hi Noob, Of course you can trust Oracle! We ...... Philip Wisse Aug 14, 2020, 18:32
Hi Philip <pre> I am currently having an issue...... sze jie koh Aug 15, 2020, 05:33

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Subject: RMAN ckpn SCN and cumulative differential backup
Author: sze jie koh, Singapore
Date: Aug 06, 2020, 15:25, 110 days ago
Os info: Solaris 11
Oracle info: 19.6
Message: Hi all

I need to understand several concepts in rman recovery and cumulative incremental backup

1) can i check what is the actual meaning of Ckp SCN and Ckp Time when you do a list backup ?

reading from documentation ->

Ckp SCN -> The checkpoint of the data file when it was backed up. All database changes before the SCN have been written to the file; changes after the specified SCN have not been written to the file.

Ckp Time -> The checkpoint of the data file when it was backed up. All database changes before the time have been written to the file; changes after the specified time have not been written to the file.


In my rman output, i am seeing all the dataflies in a backupset having the same ckp time / ckp scn

How is that possible ?

The datafiles that are being backup are quite hugh and will take sometime to backup, meanwhile i am sure that are continous commit and checkpoint made to those datafiles


2) When a cumulative differential backup is done by rman - does rman looking at the individual blocks in the datafiles of the most recent level 0 backup and compare against the current datafiles it is backing up ?

reading from documentation ->

Each data block in a datafile contains a system change number (SCN), which is the SCN at which the most recent change was made to the block. During an incremental backup, RMAN reads the SCN of each data block in the input file and compares it to the checkpoint SCN of the parent incremental backup. If the SCN in the input data block is greater than or equal to the checkpoint SCN of the parent, then RMAN copies the block.


is this "checkpoint SCN of the parent" referring the Ckp SCN earlier on in q1 ?


3) if a level 0 backupset has datafiles with e.g. checkpoint SCN of 1111 and a level 1 incremental cumulative backupset has datafiles with checkpoint SCN of 3333

Does that means archivelogs between SCN 1111 to 3333 are not required at all if i want to do a point in time recovery to > SCN 3333 ?

Thank you
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Subject: Re: RMAN ckpn SCN and cumulative differential backup
Author: Philip Wisse, Netherlands
Date: Aug 10, 2020, 17:46, 106 days ago
Message: Hi Noob,

1) Not sure, rman internals; you can guess about them but behaviour may change.
I guess the datafile header is read only once at the beginning of the backup.
When writing data rman first has to open a channel (or multiple channels) and hand off writing the data to a backup slave(s)
2) No, 'the parent' meaning 'parent incremental backup' as in the sentence before.
In case of an incremental backup rman can use a block tracking file if you have created one before the full backup.
3) True, rman will automatically decide which path to follow when recovering.

Regards, Philip
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Subject: Re: RMAN ckpn SCN and cumulative differential backup
Author: Philip Wisse, Netherlands
Date: Aug 13, 2020, 15:42, 103 days ago
Message: #3 Adding a reference:
https://docs.oracle.com/database/121/BRADV/rcmcncpt.htm#GUID-C93F3588-BBA9-4AE2-9E47-74C7A9468023

It says: "About Recovery with Incremental Backups:
During media recovery, RMAN examines the restored files to determine whether it can recover them with an incremental backup. If it has a choice, then RMAN always chooses incremental backups over archived redo logs because applying changes at a block level is faster than applying redo."
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Subject: Re: RMAN ckpn SCN and cumulative differential backup
Author: sze jie koh, Singapore
Date: Aug 14, 2020, 07:03, 102 days ago
Message: Hi Philip

1) so do you think i should not pay attention to this ckp scn ? can i trust this ckp scn in the list backup as the baseline that all data before this scn is already written to the datafile and is contain in the backup


I am currently having an issue - whereby i obviously have
- level 0 backup - at 27th 0020 hrs
- level 1 cumulative backup at 29th 0020 hrs
- all archivelogs of the entire day of 29th

when doing a restore preview until time 29th 0900hrs - rman prompted it requires archivelogs from 27th as early as the ckp scn in the list backup

Do you have any idea why is this so ?

Thank you
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Subject: Re: RMAN ckpn SCN and cumulative differential backup
Author: Philip Wisse, Netherlands
Date: Aug 14, 2020, 18:32, 102 days ago
Message: Hi Noob,

Of course you can trust Oracle!

We all know checkpoint nowadays are not the same anymore as they used to be. But what is a lazy checkpoint? It's just the least possible work to be done by the db writer.

One thing to check how in the alert.log the end time of the checkpoint relates to the start time of the backup.

Regards, Philip
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Subject: Re: RMAN ckpn SCN and cumulative differential backup
Author: sze jie koh, Singapore
Date: Aug 15, 2020, 05:33, 101 days ago
Message: Hi Philip


I am currently having an issue - whereby i obviously have
- level 0 backup - at 27th 0020 hrs
- level 1 cumulative backup at 29th 0020 hrs
- all archivelogs of the entire day of 29th

when doing a restore preview until time 29th 0900hrs - rman prompted it requires archivelogs from 27th as early as the ckp scn in the list backup

Do you have any idea why is this so ?


Do you have anything in mind ? - base on the scenario above - do we need any archivelogs on 27th to recover until 29th 0900hrs ?

Thank you
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