Re: Dynamic Performance Views from Control Files

V$s are views on 'virtual tables' that are constructed and populated when you start your Instance. They are not, technically, part of the data dictionary, but most people would think of them that way (myself included) -they are views on these special virtual tables, not on the usual x$ tables of which the real data dictionary is comprised.

What your book is saying is that having built these virtual tables, where does Oracle get the information to populate them? And in the case of the ones you listed, the controlfile is indeed to source. The control file has various 'sections' dedicated to things like pointing at the various datafiles, or marking which tablespaces are in hot backup mode. You can see all the various sections by querying the v$controlfile_record_section view.

If you think about it, this is clearly the case for some of the views in particular. When you move a datafile from disk 1 to disk2, for example, you use the 'alter database datafile '/disk1/system01.dbf' to '/disk2/system01.dbf' to make the change -and it's generally the case that whenever you issue an 'alter database' command, it's actually the controlfile that you are talking to. So clearly, datafile locations must be stored in the Control File.

So, the full story must be that the virtual tables are created at startup, then at Mount stage, Oracle reads the Control File contents, and uses the information it finds there to populate those particular tables.

Regards
HJR

--
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The views expressed are my own only, and definitely NOT those of Oracle
Corporation
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"Victor Lung" <victorlung_at_hotmail.com> wrote in message
news:9edqbm$8s15_at_imsp212.netvigator.com...


> I have read the following statement in the oracle book.

>

> The information in several of the other dynamic performance views is

> obtained

> from the control file:

> V$BACKUP

> V$DATAFILE

> V$TEMPFILE

> V$TABLESPACE

> V$ARCHIVE

> V$LOG

> V$LOGFILE

>

> Does it mean these information or views are retrieved from control file,

 but


> not from data dictionary?

>

> Is data dictionary is only views from the base table? does it have any

> relationship with control file?

>

> thx!!

>

>