0 Logical Backups

  • Logical Backups can be taken by 1)Tables 2) Users 3) Full database
  • Logical backup works as an alternative backup system.
  • The beauty about logical backup is we can be selective(which means we can backup/restore only the required objects which cannot be possible with physical backup)
  • Logical backup also offers incremental backup style
  • From oracle 8i we can export huge database to multiple dump files(Across systems)
  • From oracle 8i we can implement transportable tablespace using exports
  • From 10g we have advanced version of export know as pump
  • Export creates two files 1)Dump file 2)logfile(Optionall)
  • Export can be used to copy objects from one schema to another schema
  • Export can also be used for copying objects from one database to another database
  • Export dumpfile is platform independent so that we can export from one operating system to another and transfer the dump file using FTP to target server with same or different operating system followed by importing
  • When we go for oracle version updates it is highly recommended to take a full database export as a safety precaution.
  • As the database gets fragmented over a period of time because of transactions, we suppose to perform database level reorganization(REORG)-usually between 3 to 4 months.For this reorg process we follow
  1. Full export
  2. Drop existing database
  3. Create brand new databasse
  4. full import
  • While export or import,we can mention dfferent options like
  1. Table name
  2. Indexes
  3. Grants
  4. rows
  5. Compresses
  6. Feedback
  • The export dump file size is usually 8 to 10 times less than the database size.Reasons below
  1. System tablespace-not exported
  2. temporary tablespace-not exported
  3. undo-not exported(As it contains before image) where we export only the committed data.
  4. Index-only definitions are exported but not the data.Because of all above reasons the dump file is so small when compared to the database size.
  • Logical Backup takes more time when compared to physical backup
  • Import is 6 to 8 times slower than export as
  1. Export is only selecting data
  2. Import has to 1)Create table 2)Insert data 3)Indexes need to be created 4)constraints are to be enabled
  • Where we migrate from one platform to another then inorder to transfer the database we have to go with export/import.

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