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Backup - Compress Backups

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• Backup - Compress Backups
  • Unsed Block Compression
    • Block Compression
    • Binary Compression Algorithms of Backup Sets
    • Syntax
  • Lab: Compressing Backup using High Algorithm

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Unsed Block Compression

Block Compression

• high-water mark:

  • the point in a segment beyond which data blocks are unformatted and have never been used.未格式化或从来未用过
  • A full table scan reads all blocks below the HWM as per definition.

• Low high-water mark:

  • the point below which all blocks are in formatted state because they either contain data or formerly contained data.曾经装有或现在有数据

• Unsed Block Compression:

  • used to save backup space
  • skips blocks:
    • Unallocated blocks:
      • the blocks are above the high-water mark (HWM).未格式或未用过
    • Unused blocks:
      • the blocks that have been allocated but no longer belong to a seament.
      • If:
        • No guaranteed restore points are defined.
        • The data file contains data only for locally managed tablespaces. 数据文件只用于本地 tbsp
        • The data file is being backed up to a backup set as part of a full backup or a level 0 incremental. 数据文件已经全备份
        • The backup is going to disk, or Oracle Secure Backup is the media manager.

• Block Compression

  • decreases the number of blocks
  • used to algorithmically compact the data that is written. 压缩数据

• Block Compression do not need to perform any additional steps when restoring a compressed backup. 恢复压缩备份时, 无需额外动作.

• Perfomance

  • Compression and Decompression operations require CPU resources.需要 CPU 资源
  • both creating and restoring a compressed backup will probably take longer and require more system resources
  • When choosing an algorithm, consider your disk space in addition to dynamic system resources such as CPU and memory.

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Binary Compression Algorithms of Backup Sets

• RMAN can perform binary compression on any backup set that is generated. 只适用于 backup set

• Compression Algorithms:

  • BASIC:
    • the only mode does not require the Oracle Advanced Compression option.
    • Fair. Compression ratio similar to MEDIUM at expense of additional CPU usage.
    • Compression ratio between MEDIUM and HIGH.
  • LOW:
    • Fastest. Best suited to address backup: CPU resources.
  • MEDIUM:
    • Fast Good balance of CPU usage and compression
  • HIGH:
    • Best compression ratio at the expense of high CPU, consumption. Best suited to address backup constraint: network.

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Syntax

• Command BACKUP AS COMPRESSED BACKUPSET if not necessary if the a global configuration is done.

-- By default
CONFIGURE COMPRESSION ALGORITHM 'BASIC' AS OF RELEASE 'DEFAULT' OPTIMIZE FOR LOAD TRUE ; # default

-- Configure compression per device
CONFIGURE COMPRESSION ALGORITHM 'HIGH/MEDIUM/LOW/BASIC';

-- Set compression individually
run {
SET COMPRESSION ALGORITHM 'HIGH/MEDIUM/LOW/BASIC'
}

-- use compression for a particular backup device
BACKUP AS COMPRESSED BACKUPSET DATABASE PLUS ARCHIVELOG;

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Lab: Compressing Backup using High Algorithm

-- configure algorithm
CONFIGURE COMPRESSION ALGORITHM 'HIGH';

-- backup
BACKUP AS COMPRESSED BACKUPSET DATABASE PLUS ARCHIVELOG;

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Comparison:

	Basic	High
ORCL	1.44G	257.54M
pdbseed	554.55M	89.26M

-- reset configuration
CONFIGURE COMPRESSION ALGORITHM CLEAR;
-- confirm
SHOW COMPRESSION ALGORITHM;

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