Q
Manage Learn to apply best practices and optimize your operations.

Questions about user-managed hot backups

I am having doubts about user-managed hot backups. Why does Log Writer write block images of changed blocks of the datafile in backup mode to the redo log instead of just the row information? Ultimately during recovery all the archived redo log files are applied to the restored files (after its log sequence number at the time of backup).

I am having doubts about user-managed hot backups. Why does Log Writer write block images of changed blocks of the datafile in backup mode to the redo log instead of just the row information? Ultimately during recovery all the archived redo log files are applied to the restored files (after its log sequence number at the time of backup). Can you please explain this? Thanks.

When you are copying an active datafile, the datafile contents may be changed while you are copying the data to your backup location. This means that your backup will be "inconsistent." The last part of the backup may contain newer transactions and the first part may contain older transactions. To solve this problem, you must be running in Archive Log mode so that Oracle can recover any transactions made while you were performing your backup.

While copying a block of a datafile, it is possible that the block may be inconsistent. This is called a "fractured block." It is possible that a row in that block may be inconsistent as well. Part of that row is old in your backup and part of the row is new in that backup. Oracle decided the best way to handle a fractured block is to write an image of that block to the archived redo log. On recovery, Oracle does not have to figure out which row is inconsistent since it replaces the entire block.

Dizwell Informatics has some great information on this as well.

Dig Deeper on Oracle database backup and recovery

Have a question for an expert?

Please add a title for your question

Get answers from a TechTarget expert on whatever's puzzling you.

You will be able to add details on the next page.

Start the conversation

Send me notifications when other members comment.

Please create a username to comment.

-ADS BY GOOGLE

SearchDataManagement

SearchBusinessAnalytics

SearchSAP

SearchSQLServer

TheServerSide.com

SearchDataCenter

SearchContentManagement

SearchHRSoftware

Close