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Online backup and the Redolog mechanism

Hello,

During a backup I understand that the redolog mechanism changes, so that when a block is changed for the first time after the backup commences, it's entire content is copied to the redolog files, rather than just the change vector.

My question is, does this happen even when the oracle block size is the same as the operating system block size?

My understanding is that the change in redolog mechanism is because a single oracle block can be made up multiple operating system blocks, so that within an oracle block a change can be done to a few blocks, then a read by the online backup, so that the oracle block read by the backup is inconsistent.

But if the oracle block size was the same as the operating system block size, each change would be atomic, so the problem of having inconsistent oracle blocks would not arise. So the change in redolog mechanism would no longer be necessary. Does the redolog mechanism change anyway?

Kind regards,

Peter

Former Member
Former Member replied

But if the oracle block size was the same as the operating system block size, each change would be atomic, so the problem of having inconsistent oracle blocks would not arise. So the change in redolog mechanism would no longer be necessary. Does the redolog mechanism change anyway?

<b>Yes, even with a filesystem blocksize same as oracle blocksize the full block goes to the redo.</b>

(which raises the other question of how to change the block size in OSes).

<b>Filesystem blocksizes depend on the os, and can be changed at filesystem creation time (at least on unix like platforms).</b>

Regards

Michael

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