Re: OT RE: RMAN Questions

On 07/10/2004 10:58:33 PM, "Mohan, Ross" wrote:
> Mladen, 
>  
> In metaphorically de-referencing a backup thread as a rope, and then
> comparing
> to OPS, RAC, etc. you are possibly forcing the generic, helpless, anonymous

There is no such thing as a "backup thread". In this context, thread is an
instance in a shared database configuration. Each instance has its own set of
redo logs, which is why there are those little nasty %t and %T format characters
in LOG_ARCHIVE_FORMAT parameter. Oracle databases have a thing called SCN, 
which 
stands for "System Change Number". SCN is increased whenever a global, atomic 
change
occurs in the database. An example is the commit event, but SCN is more general 
then
just being a commit counter. Oracle database uses SCN to account for the block 
versions,
in order to ensure the transaction consistency. In a shared database system, 
there 
are two SCN numbers: local and global. Global SCN is used for synchronization 
purposes, and 
it is written to the redo logs and,  consequently, to the archived logs. The 
command that the original author of the question  was referring to was: 

restore database until sequence 100 thread 1; 

Restore the database and include all blocks whose SCN numbers are less then the 
smallest 
global SCN in the archived log with sequence 100, coming from the thread 1.


Obviously, reading manuals presents an insurmountable obstacle to some hapless 
people.
That being the case, let me post an excerpt from the RMAN manual referring to 
that specific syntax:
************************************************************************************************

Keywords and Parameters
Syntax Element  Description

UNTIL SCN = integer
        

Specifies an SCN as an upper limit. RMAN selects only files that can be used to 
recover up to but not including the specified SCN. For example, RESTORE 
DATABASE UNTIL SCN 1000 chooses only backups that could be used to recover to 
SCN 1000.

UNTIL SEQUENCE = integer THREAD = integer
        

Specifies a redo log sequence number and thread as an upper limit. RMAN selects 
only files that can be used to recover up to but not including the specified 
sequence number. For example, REPORT OBSOLETE UNTIL SEQUENCE 8000 THREAD 1 
reports only backups that could be used to recover through log sequence 7999.
************************************************************************************************

Now that we've cleared the mess around RMAN, SCNs and shared database systems, 
being OPS or RAC,
it is my turn to ask what purchasing decision are you talking about? Ropes are 
not that expensive,
and if used the right way, the family shouldn't be very unhappy. DBA who uses 
this list as a
basis for major purchasing decisions, without knowing what the database thread 
is, is not likely
to have many people mourning him. Also, as a DBA, I intensely dislike people 
posting trivial
questions to this list, because it diminishes this usefulness for me. I 
strongly suggest 
reading the manuals before posting a trivial question to this list. I know what 
tha majority
thinks about it and I don't care. I practically withdrew from the list and I my 
main forum 
is the Usenet group, but occasionally, when I have a very bad day, a poster of 
trivial questions
is likely to get stung. If you don't like it, you should block my post. As far 
as I remember,
OE has "block sender" button and I suggest you to use it.

-- 
Mladen Gogala
Oracle DBA
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