gboyapalli

 Profile Answers by gboyapalli 

• Mar 13th, 2008

 

A block fracture occurs when a block is being read by the backup and bieng written to at the same time by the DBWR. This happens because OS reads blcoks at a different rate than Oracle. your OS copy will pull pieces of an Oracle block at a time. What if the OS copy pulls half a block, and while that is happening, the block is changed by DBWR? When the OS copy pulls the second half of the block it will result in mismatched halves, which Oracle would not know how to reconcile. This is also why the SCN of the datafile header does not change when a tablespace enters hot backup mode. When receovery occurs the fractured data file block will be replaced with a complete block from redo.

I hope this helps;

-GB

alok83

 Profile Answers by alok83 

• Apr 11th, 2008

 

The concept of fractured block occrus when backup is under process.
It means you are taking backup and some other session is updating it.
Then backup process can not get the consistent image of the block and it will be inconsistent right thats why it is called fractured block.

ganesh

• Mar 12th, 2013

 

In case of hot backup we get fractured blocks, because of this reason hot backups is called Inconsistent backup.
let say in hot backups our operating system copies OS block by OS block while copy is going on our dbwr (data writer) is modifying by block that means we are getting fractured block...50% of block is going to backup destination and rest of the 50% block is modified by dbwr. so we get fractured block or inconsistent block..
the solution that was given by oracle for this is whenever we take a hot backup keep the table spaces in a special mode that we called as a begin backup mode..

Regards
Ganesh