Journal is a mechanism of securing data by maintaining a copy of data securely. It is a kind of record activity.

Types of Journals :

Recovery Journal :
  • Single Image ( Maintains one copies of Image )
  • Automatic:Automatically activated when an amp is taken off-line
  • Maintained by other amps in the cluster
  • Totally transparent to users of the system.
         While AMP goes off-line :
  •        Journal becomes active
  •        Table updates continue as normal
  •         Journal logs row_id s of changed rows for down amp
         When AMP comes on-line:
  •              Restores rows on recovered amp to current status
  •              Journal discarded when recovery complete
Transient Journal :

The Transient Journal (TJ) protects against failures that may occur during transaction processing automatically and transparently. To safeguard the integrity of your data, the TJ stores:
  •           Dual Image ( Maintains two copies of Image )
  •           Automatically rolls back data to original values if you abort the transaction or there is a restart.
  •      A snapshot of a row before an UPDATE or DELETE
  •            The Row ID after an INSERT
  •      The control record for each CREATE and DROP statement
  •      BEGIN and END TRANSACTION images
If a transaction is aborted or fails, the TJ enables the database to be restored to the state it was in before the transaction began. Its contents are used to:
  •      Copy snapshot rows back into their tables
  •       Remove inserted rows
  •             Delete partially created objects, or rebuild and, if necessary, repopulate dropped objects
  •       FastLoad and MultiLoad jobs do not write to the TJ for individual rows and do not use the TJ to keep track of changes.

Permanent Journals :

The purpose of a Permanent journal (PJ) is to maintain a sequential history of all changes made to the rows of one or more tables. PJs help protect user data when users commit, uncommit, or abort transactions. A PJ can capture a snapshot of rows before a change, after a change, or both.

  •       Dual Image ( Maintains Objects before change and After object change)
  •       It is a Manual Operation .
Use PJs to protect against the following:
  •       Loss of data caused by a disk failure in a table that is not fallback or RAID protected
  •       Loss of data if two or more AMP V-Procs fail in the same cluster. This would mean the loss of two disks in a rank per failed AMP Virtual processor (V-Procs )
  •       Incorrect operation of a batch or application program
  •      Disaster recovery of an entire system      
  •            Loss of changes made after a data table is archived
  •           Loss of one copy of the journal table (with dual Journaling ).


Single Image
    Captures/stores one copy of the data

Dual Image
    Captures/stores two separate copies of data: one copy on the primary AMP and one on the fallback

Before Image
Captures/stores row values before a change occurs..
After Image
Captures/stores row values after a change occurs.