Re: online backup

Hi Alvin,

after the "begin backup" command, oracle will prevent the headers of the data file to be written to.
Data blocks are (!!) written to the files (and of course to the redo-log files with some additional info during backup time). This is done to ensure a definite point for recovery to start. If you ever have to restore a datafile, Oracle will check the header of the datafile against the information in the control files and apply all redo logfiles (archived and online) which are older than the information in the controlfile but younger than the information in the datafile header. The blocks are written to the datafile, to ensure that changes are in the datafile.

If you switch from begin backup to end backup, headers are free again and the next checkpoint will overwrite the old header and from now on the modified rows in the datafile(s) are valid. Subsequent shutdown / startup sequences will not apply any redologs. If the checkpoint has not already run before the database goes down, then a recovery will occur at startup time.

Hope this helps.
Andy

Alvin schrieb:

> hi,all
> when I do online backup,after the command
> alter tablespace abc begin backup;
> if I modify data in the tablespace abc,what will happen??
> ORACLE will store modified data in somewhere else?? or .....
>
> THx
>
> Alvin Huang
Received on Mon May 29 2000 - 00:00:00 CDT