Re: x$ constructs and memory

No, X$ tables exist even before a database is created -> they are mostly instance related structures, not database or data dictionary ones. Do a startup nomount and select from x$ksuse or even dual for example and you see.
You just can't select from these x$ tables which want to read physical database structures when database doesn't exist or isn't mounted/open. The translation of SGA memory structures to a returnable row set is pure C code, I think.

Or if you can point me to these "certain catalog scripts", I'd be glad to read them :O)

But yes, about the "fixed area" I wasn't entirely correct at first. The Oracle term "fixed_sga" is really fixed, that it's size shouln't change if you don't relink of patch your executables. x$version contents are probably in fixed_sga. The other stuff, like enqueues goes to variable SGA (shared pool), but still many memory structures are not dynamic - they're allocated during startup and will remain the same during the lifetime of an instance.

Tanel.

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Monday, September 29, 2003 9:24 PM

> With all due respect, I don't believe that it is a fixed area.
> You can create X$ tables by running certain catalog scripts. I believe
> that the description of X$ tables is located logically close to the
> description of the data dictionary, which would mean shared pool, not
> the fixed one. Now, can we get back to bears?
>
> --
> Mladen Gogala
> Oracle DBA
>
>
>
> > -----Original Message-----
> > From: ml-errors_at_fatcity.com [mailto:ml-errors_at_fatcity.com] On
> > Behalf Of Tanel Poder
> > Sent: Monday, September 29, 2003 1:45 PM
> > To: Multiple recipients of list ORACLE-L
> > Subject: Re: x$ constructs and memory
> >
> >
> > > What I have not checked so far is how an ALTER SYSTEM
> > increasing a
> > parameter affects the SGA. In practice it's a realloc()
> > (functionally speaking). It would seem reasonable to me to
> > have a shared memory segment to hold all parameters which can
> > by dynamically changed. I wouldn't touch it if parameters are
> > decreased, but I would have to realloc it in case of a
> > massive increase. Hmm, I guess that I would allow some spare
> > memory initially, performance penalty would otherwise be
> > severe. Which all makes the 10g dynamic rearrangement quite
> > sensible ...
> >
> > Hi!
> >
> > I think the behaviour depends on which parameter you are
> > changing. If you're changing shared_pool_size to higher size,
> > then just additional extents of memory are allocated and heap
> > header is updated. If you set sort_area_size higher, nothing
> > particular happens, except some maximum is increased in UGA I
> > believe and during next sort you can go up to that limit.
> > Some parameters like enqueue_resources can't be changed in
> > the fly, because they are fixed, they stay in fixed area of
> > SGA, fixed area isn't managed as heap as I understand, it
> > does not have any free or LRU lists, because it's physical
> > structure remains unchanged during the lifetime of an instance.
> >
> > Tanel.
> >
> >
> > --
> > Please see the official ORACLE-L FAQ: http://www.orafaq.net
> > --
> > Author: Tanel Poder
> > INET: tanel.poder.003_at_mail.ee
> >
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> Author: Mladen Gogala
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-- 
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-- 
Author: Tanel Poder
  INET: tanel.poder.003_at_mail.ee

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