180.What are permanent journals in teradata?
- Journals are used to capture information about table in Teradata. In case of Permanent journals they capture details of Journal enabled tables in teradata with all the pre transaction and post transaction details .
- Journal tables are assigned PERM space and they reside in same database as of parent or they can reside on different database.
- They are mainly used for protection of data and sometimes also for disaster recovery ( fallback is better in this case )
- Permanent journal tables can be enabled or disabled by running alter database <databasename> ‘no journal’ /’ journal = <databasename.jrnltbl>’
- Arcmain utility provides the feature of backing up Journal tables
- We can find details about all journal tables present in teradata database using DBC.JOURNALS table.
181.what are different types of journals in teradata?
There are 3 different types of journals available in Teradata.
- 1. Transient Journal – This maintains current transaction history. Once the query is successful it deletes entries from its table . If the current query transaction fails, It rolls back data from its table.
- 2. Permanent Journal – This is defined when a table is created. It can store BEFORE or AFTER image of tables. DUAL copies can also be stored. Permanent Journal maintains Complete history of table.
- 3.Down AMP recovery Journal (DARJ) – This journal activates when the AMP which was supposed to process goes down. This journal will store all entries for AMP which went down. Once that AMP is up, DARJ copies all entries to that AMP and makes that AMP is sync with current environment.
182.What are benefits of Permanent Journal?
- Permits capture of before images for database rollback.
- Permits capture of after images for database roll forward.
- Permits archiving change images during table maintenance.
- Reduces need for full-table backups.
- Provides a means of recovering NO FALLBACK tables.
- Requires additional disk space for change images.
- Requires user intervention for archive and recovery activity
183.What is the purpose of Before Journal and After journal?
We use both before journal and after journal in Permanent journal to do selective or full recovery of data
184.Where does TD store transient journal?
In perm space -> dbc.transientjournal
But that special table can grow over dbc’s perm limit until the whole system runs out of perm space.