Re[2]: Common Oracle RDBMS Misconceptions

Joe & company,

    Jeremiah has it exactly correct. The only part of the data file that is "un-writable" is the datafile header block, which gets frozen until the hot backup of that tablespace completes. Look at it this way, when the "start backup" command gets issued Oracle is in fact freezing that datafile(s) at that point in time and assuming that all changes to the datafile(s) have not been written. When you restore the file, you then apply redo from your archive logs (the reason you MUST be in archive mode) from the start of the backup till the end of the recovery just as if those changes to the file(s) had never been made in the first place. In fact Oracle knows the changes were made during the backup, it just has no idea if the change was written to the file before or after your backup software copied that portion of the file to tape or wherever. Therefore, simple solution assume it was after. In practice the process is very simple, does slow the database down a tad, and works as advertised. (Been there, done that several times.)

BTW: IMHO, don't waste your money on any of the SAMS books. They are full of similar misconceptions.

Dick Goulet

____________________Reply Separator____________________
Author: "Joseph S. Testa" <teci_at_the-testas.net>
Date:       6/26/2001 4:00 AM

Well i dont know about everyone else, but i knew thats how the hot backup worked, but then again, i've not attended oracle education classes either, just some hard core reading and have gotten all of my backup/recovery concepts from Rama Velpuri's book. An excellent book if you dont have it.

joe

> On Jun 26, 2001 at 01:05:59AM, novicedba wrote:
> > Hi everyone,
> > I visited Jeremiah Wilton's web page http://www.speakeasy.net/~jwilton
> > I was shocked to read Hot backup mode explained
> > If this is true then I may be a victim of a disease called
> > 'Common Oracle RDBMS Misconceptions' . Somebody help me!! (Jim carrey-MASK
style)
> > Please help me. If some one has few more articles like this enlighten me

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