Re: Request for information from V7.0 DBA Volume II on backup

In a previous article, moy_at_quek.enet.dec.com () says:

>The ALTER DATABASE BEGIN BACKUP command does the following:
>
> 1) stalls new update requests
> 2) waits until all existing update transactions are done
> 3) prevents new update requests from updating the database files
> (they go to the redo log)
> 4) permits new update requests to continue

No no no no no nooooo.....

The ALTER TABLESPACE BEGIN BACKUP command does the following:

1. Disables the updating of the timestamp in the database file header block when checkpoints occur.
2. Writes a special entry into the redo log denoting the beginning of the backup.
3. Causes whole database blocks to be written to the redo log during the backup (unless init.ora parameter LOG_BLOCKS_DURING_BACKUP=FALSE).

The ALTER TABLESPACE END BACKUP command does the following:

1. Brings the timestamp in the data file header block up to date.
2. Writes a special entry into the redo log denoting the end of the backup.
3. Causes the writing of the redo log to go back to normal (only changed data in the block is written to the log).

>thanks,

   No Problem.

-- 
   - Doug Harris
     Database Administrator,
     System Development Division,
     Statistics Canada             ### Standard Disclaimer Applies ###