Journal is a mechanism of securing data by maintaining a copy of data securely. It is a kind of record activity.
Types of Journals :
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
- 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 ).
Option
|
Description
|
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.
|
0 Comments