Re: why r more archives generated during hot backup

bookmark worthy explanation

tks Richard

"Richard Foote" <richard.foote_at_bigpond.com> wrote in message news:<AYAi9.36435$g9.103745_at_newsfeeds.bigpond.com>...
> Hi Cane001,
>
> To protect the database from "fractured blocks".
>
> As you're performing an OS copy at the same time Oracle is writing to the
> data files, the possibility exists that a portion of an Oracle block is
> copied, followed by the DBWR overwriting the particular block , followed by
> the remaining portion of the Oracle block being copied. This means the
> copied Oracle block has a split personality in that one portion of the block
> is from one point in time and another portion of the block is from a
> different point of time.
>
> In other words, a fractured block.
>
> Restoring such a block would prove to be unrecoverable with the usual
> generation of redo as there is no way to reconstruct the block in a
> consistent manner.
>
> Therefore, while a data file is in hot backup mode, Oracle prevents issues
> with fractured blocks by coping the before/after image of the entire block
> such that an entire consistent block can be used during the recovery
> process.
>
> This is one of the reasons why it's vital to place the tablespace in backup
> mode before attempting a hot backup.
>
> This excessive redo generation is also the reason why it's recommended where
> possible to place one tablespace at a time in backup mode and why hot
> backups should be performed during a quiet period.
>
> Note that RMAN doesn't concern itself with this issue as fractured blocks
> are not possible with RMAN. That's because RMAN performs a checksum test on
> each block as it performs the copy. If it fails this test, RMAN simply
> recopies the block. If it passes the test this time, it was obviously a
> fractured block which the immediate recopy has automatically remedied. If it
> fails for a second time, then it's a corrupted block which RMAN duly
> documents.
>
> Cheers
>
> Richard
> "Cane001" <nkapadia41_at_yahoo.com> wrote in message
> news:acf7ab77.0209200004.72143f7f_at_posting.google.com...
> > I would like to know why r more archives generated during hot backups
Received on Fri Sep 20 2002 - 13:17:18 CDT