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Why Incremental accumulative backup has the same size as a full backup

Mitya HORT
Mitya HORT Member Posts: 17 Green Ribbon
edited Oct 26, 2021 7:23AM in General Database Discussions

Hi Team,

Do you use to face the issue like me or not. I have 2 backup type.

  1. Is full backup which is backup every Monday - size arround 60GB
  2. Is incremental accumulative backup is backup from Tuesday to Sunday , size of backup should me around 3GB ( backup only block change). but i notice that every two days system is backup size same as full backup ( size = 60GB) even script is used for incremental accumulative backup. but the same script was applied with other database environment system is working properly meaning that On Monday size of backup is full and Tuesday to Sunday size of backup is incremental accumulative backup.

Thank,

Mr. Mitya

«1

Comments

  • Mike Kutz
    Mike Kutz Member Posts: 5,819 Silver Crown

    I'm curious about the backup lines used in your RMAN script.

    You may want to post your full DB version.

    It's been awhile since I managed backups. All these are from my flawed memory when I was on 11.2.0.3

    Every week, Oracle would do something that would cause (what seemed like) every row in every table to be rearranged. (We were licensed for Advanced Compression so full backups weren't a problem)

    /*+ APPEND */ steps had a habit of invalidating tablespoons. These had to be "full backup" "manually" in order to ensure my backups worked as expected. (I had a script to level 0 incremental backup specific tablespaces)

  • EdStevens
    EdStevens Member Posts: 28,532 Gold Crown

    First, it would help if you actually posted the backup scripts, as copied/pasted text, formatted and code-blocked.

    Beyond that I'd point out that cumulative (not accumulative) backups have all the changes since the last full/incremental 0 backup. So I'd expect each successive one to get larger than the previous. If you want the daily incremental backup to remain small, then you would take an incremental differential backup. The trade-off is that the differentials will take less disk space, but require more pieces to be applied in the event of a recovery.

  • Mitya HORT
    Mitya HORT Member Posts: 17 Green Ribbon

    Hi All,

    This is script backup for level 1

    backup AS COMPRESSED BACKUPSET incremental level 1 cumulative database;

    It is make sense if size of backup is small because in daily data is not change much. and if size same as full backup level 0 is not make sense. The same script was applied with another database instance is working fine. except this one raised. do you face same issue like me?

    Database version : 12.2.0.1.0

    Regards,

    Mr. Mitya

  • EdStevens
    EdStevens Member Posts: 28,532 Gold Crown

    Is that one line the entire script? In any event, in addition to any script, we'd need to see the basic settings - an rman 'show all' while connected to the target database.

  • EdStevens
    EdStevens Member Posts: 28,532 Gold Crown

    I just copy one line of syntax incremental accumulative backup

    This is like pulling teeth. If we want to know how a particular backup operation is behaving, we need to see the entire script, as well as the configuration settings. A runtime log of the backup could be helpful as well.


    but i notice that every two days system is backup size same as full backup

    Perhaps every two days you have some operation that touches most of the blocks, thus causing nearly a full backup. And again, a cumulative backup gets all of the blocks that have been changed since the last full/incr 0 backup. So I'd expect each successive cumulative backup to be larger than the previous, until you take a new full/incr 0 backup.


    Day 1 - Incremental 0 (full) backup.

    Day 2 - since yesterday, only block id= 1 has changed so the cumulative backup gets only that block.

    Day 3 - since yesterday, only block id = 2 has changed, but we are taking a cumulative backup, so we get blocks 1 and 2.

    Day 4 - since yesterday, only block id = 3 has changed, but we are taking a cumulative backup, so we get blocks 1 and 2 and 3.


    etc, etc, etc.

  • EdStevens
    EdStevens Member Posts: 28,532 Gold Crown

    Depends on how many blocks were touched.

    But I see a very important problem with your script. First, even your 'backup' command itself is much more complex than what you first indicated, when you tried to show 'just' the backup command.

    More importantly, you are manually creating your own directories in the FRA, then specifying those specific directories in your backups. Why are you doing this? This bypasses the bookeeping of the FRA space, so that your FRA will always have less actual disk space than it thinks it has. You should simply configure your FRA size and location (one time setup in the DB), then let everything default to the location that oracle wants to use. The whole idea of the FRA is that oracle - not the DBA - manages everything in it.

    You are also writing your rman log files into the same directory as used by the FRA, but this is NOT an FRA-managed file.

  • Mitya HORT
    Mitya HORT Member Posts: 17 Green Ribbon

    i dont get your idea.

  • EdStevens
    EdStevens Member Posts: 28,532 Gold Crown

    I'm afraid you will have to be a bit more explicit about what it is you do not understand.

  • tsangsir
    tsangsir Member Posts: 449 Silver Badge
    edited Oct 29, 2021 5:11AM

    What's the result of following query?

    select trunc(bs_completion_time) completion_date, file_type, bs_incr_type, round(sum(bytes)/1048576) mb
    from V$BACKUP_FILES
    where bs_completion_time > trunc(sysdate)-7
    group by trunc(bs_completion_time), file_type, bs_incr_type
    order by trunc(bs_completion_time) desc, round(sum(bytes)/1048576) desc;
    


    EdStevens
  • Mitya HORT
    Mitya HORT Member Posts: 17 Green Ribbon

    Hi tsangsir,

    Please kindly find the attached file on 29-Oct-2021, data should be less than 3GB because it is incremental accumulative backup. It is not backup sense . Full backup is only every Monday.

    Thank.