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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