Re: relation bet REDO LOG FILE and BEGIN BACKUP

"sybrandb" <sybrandb_at_yahoo.com> wrote in message news:1152605925.870552.276390_at_m79g2000cwm.googlegroups.com...
>
> peter wrote:
>> Hello DBAs,
>>
>> when we issue
>> alter tablespace <tb_name> begin backup;
>> what extra information go in redo log, why archive is fast and if there
>> is shutdown abort why backup at that time is not useful........
>>
>> Because in books it was mentioned that archive is fast because all
>> information of tablespace would go in redo log but even in simple way,
>> everything goes in redo log so what extra..........
>
> According to the documentation, begin backup forces Oracle *for every
> change* to write the complete block to redolog, instead of changed
> bytes only.
>
>
> --
> Sybrand Bakker
> Senior Oracle DBA
>

If that's what the manual says, it's wrong. 'begin backup' forces a tablespace checkpoint.

After the checkpoint is complete, the first change to a block after it has been loaded into the cache (or the first change for any block already in the cache) causes a complete block write of the current version of the block, followed by the normal redo. Subsequent changes __while the block stays in the buffer__ do NOT cause a further block write.

-- 
Regards

Jonathan Lewis
http://www.oracle.com/technology/community/oracle_ace/ace1.html#lewis

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