Re: benefits of multiple switch logfile calls?

Doing even 1 "switch logfile" makes no sense, especially when you consider that the command comes back instantly but the LGWR process might not finish for a minute or 2 (depending on how fast LGWR copies the REDO).

This would be a problem when the next thing your backup is doing is probably (or should be) copying the archived redo logs . So, the copy of the archived redo log being created by LGWR might be changing by LGWR while you are copying.

I wonder if the problem with your test recover is that you do not do an "alter system checkpoint;" to dump the buffered REDO uncommitted log information before doing the archive log current?

The old backup would have maybe not had a similar problem because the "switch logfile" causes a checkpoint (I think) and so as long as the copy of the archived redo log was done after LGWR was finished , you would have been ok.

-- 
"Don Seiler" <don_at_seiler.us> wrote in message
news:pan.2003.12.03.19.10.01.379872_at_seiler.us...


> Testing hot backup strategy for Oracle 9.2.0.4.  Due to space concerns I'm

> not using RMAN right now, just putting tablespaces in backup mode and

> gzipping datafiles to backup dir, similar to what we do now in Oracle

> 7.3.4.5.

>

> One problem I have is that my test recover failed complaining that it

> needed to apply more archive logs.  The logfile it asks for was not

> created.  In my new backup script I call "ALTER DATABASE ARCHIVE LOG

> CURRENT" before copying over the log files.

>

> However in the Oracle 7.3.4.5 (written by wiser consultant 5 years before

> my time) script, there are three "switch logfile" statements in succession

> followed by the archive log current, literally like this:

>

>   ALTER SYSTEM SWITCH LOGFILE;

>   ALTER SYSTEM SWITCH LOGFILE;

>   ALTER SYSTEM SWITCH LOGFILE;

>   ALTER SYSTEM ARCHIVE LOG CURRENT;

>

> Would that fact that I'm not calling SWITCH LOGFILE at all (let alone

> multiple times) lead to the fact that I'm missing some redo info?  I don't

> understand why multiple calls are of any value, but I've seen it done in

> other scripts on the web and in the Oracle news groups.