Note_Tech

All technological notes.

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DBA2 - PDB Snapshot Carousel

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• DBA2 - PDB Snapshot Carousel
  • PDB Snapshot Carousel
  • Creating PDB Snapshots
    • Enable Snapshots
    • Create manual PDB snapshots
    • Disable snapshot creation for a PDB
  • Creating PDBs by Using PDB Snapshots
  • Dropping PDB Snapshots
  • Flashing Back PDBs by Using PDB Snapshots

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PDB Snapshot Carousel

• PDB Snapshot Carousel

  • a library of PDB snapshots.

• PDB Snapshot:

  • a named copy of a PDB at a specific point in time.
  • an archive file (.pdb) containing the contents of the copy of the PDB at snapshot creation.
  • allow the recovery of PDBs back to the oldest PDB snapshot available for a PDB.
  • By default, is enabled.

• Every PDB snapshot is associated with a snapshot name and the SCN and timestamp at snapshot creation.

• It extends the recovery beyond the flashback retention period that necessitates database flashback enabled.
• Use case:
  • reporting on historical data.
  • e.g.,:
    • You might create a snapshot of a sales PDB at the end of the financial quarter.
    • You could then create a PDB based on this snapshot so as to generate reports from the historical data.

• Storage-efficient snapshot clones taken on periodic basis

• MAX_PDB_SNAPSHOTS database property:
  • sets the maximum number of PDB snapshots for each PDB.
  • Default: 8. Maximum of eight snapshots for CDB and each PDB
  • When the maximum number is reached for a PDB, and an attempt is made to create a new PDB snapshot, the oldest PDB snapshot is purged.
    • If the oldest PDB snapshot cannot be dropped because it is open, an error is raised.
    • If you want to drop all PDB snapshots, you can set the limit to 0.

• On Friday, need to recover PDB1 back to Wednesday:
• Restore PDB1_snapW.

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Creating PDB Snapshots

Enable Snapshots

• By default, a PDB is enabled for PDB snapshots.

• There are two ways to define PDBs enabled for PDB snapshot creation:

  • Manually:

  -- Enable the PDB for PDB snapshots.
  CREATE PLUGGABLE DATABASE pdbl ...
  SNAPSHOT MODE MANUAL;
  

  • Automatically after a given interval of time:

    • When the amount of time is expressed in minutes, it must be less than 3000.
    • When the amount of time is expressed in hours, it must be less than 2000.

    -- pecifies that a PDB snapshot is created automatically every 24 hours.
    ALTER PLUGGABLE DATABASE pdbl
    SNAPSHOT MODE EVERY 24 HOURS;
    

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Create manual PDB snapshots

• can specify a name for a PDB snapshot.
  • can manually create PDB snapshots with a custom name.
  • If PDB snapshots are created automatically, the system generates a name.

-- mannually create a pdb snapshot with a custom name
ALTER PLUGGABLE DATABASE pdbl
SNAPSHOT pdbl_first_snap;

ALTER PLUGGABLE DATABASE pdbl
SNAPSHOT pdbl_second_snap;

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Disable snapshot creation for a PDB

ALTER PLUGGABLE DATABASE pdbl SNAPSHOT MODE NONE;

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Creating PDBs by Using PDB Snapshots

• You can create a new PDB from an existing PDB snapshot by using the USING SNAPSHOT claus Provide any of the following:
  • The snapshot name
  • The snapshot SCN at which the snapshot was created
  • The snapshot time at which the snapshot was created

CREATE PLUGGABLE DATABASE pdbl_day 1 FROM pdbl
USING SNAPSHOT <snapshot_ name>;

CREATE PLUGGABLE DATABASE pdbl_day 2 FROM pdbl
USING SNAPSHOT AT SCN <snapshot SCN>;

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Dropping PDB Snapshots

• Automatic PDB snapshot deletion when MAX PDB SNAPSHOTS limit is reached
  • There is no need to materialize a PDB snapshot in carousel, because PDB snapshots are all full clone.
  • Be aware that if the SNAPSHOT COPY clause is used with the USING SNAPSHOT clause, the SNAPSHOT COPY clause is simply ignored.

• You can manually drop the PDB snapshots by altering the PDB for which the PDB snapshots were created and by using the DROP SNAPSHOT clause.

ALTER PLUGGABLE DATABASE pdbl
DROP SNAPSHOT pdbl_first_snap;

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Flashing Back PDBs by Using PDB Snapshots

• PDB snapshots enable the recovery of PDBs back to the oldest PDB snapshot available for a PDB.

• Example:

  • detect an error that happened between PDB1_SNAPW and PDB1_SNAPT creation.
  • To recover, perform the following steps:
    1. Close PDB1.
    2. Create PDB1b from the PDB1_SNAPW snapshot created before the user error.
    3. Drop PDB1.
    4. Rename PDB1b to PDB1.
    5. Open PDB1 and create a new snapshot.

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