Re: Oracle internals.

From: Howard Rogers <dba_at_hjrdba.com>
Date: Mon, 10 Dec 2001 10:19:10 +1100
Message-ID: <YrSQ7.11$bk2.1082@inet-nntp1.oracle.com>

"Thomas Kyte" <tkyte_at_us.oracle.com> wrote in message news:9v0hvn01qac_at_drn.newsguy.com...
> In article <3c13bffb$0$2579$afc38c87_at_news.optusnet.com.au>, "Howard
says...
> >
> >Comments below.
> >HJR
> >--
> >----------------------------------------------
> >Resources for Oracle: http://www.hjrdba.com
> >===============================
> >
> >
> >"Andrej" <andrej611_at_wp.pl> wrote in message
> >news:9v0dag$9a1$1_at_korweta.task.gda.pl...
> >> Hello,
> >>
> >> I am looking for the following info concering Oracle internals:
> >> - how does Oracle know what blocks are assigned to what tables ? does
is
> >> blindly scan throug all the blocks ?
> >
> >No, it holds that information in data dictionary tables. Specifically,
UET$
> >records what extents exist, and who owns them. Tables such as OBJ$ and
TAB$
> >also come into play. In locally managed tablespace, a bitmap at the
header
> >of the tablespace indicates whether a block is reserved for use or not.
> >Data dictionary entries still say which object owns which block.
> >
> >> - I know a single block can hold data for different segments.
> >
> >No it can't.

> sure it can. CLUSTERS do just this...
>

A cluster (we're talking index clusters here, naturally) is a segment. Therefore, the block still holds entries relating to one segment.

If you create a cluster called BLAH_CLU, and create an emp and a dept table within that cluster, a select from dba_segments will list BLAH_CLU, buit not sight nor sound of an EMP or DEPT table.

Regards
HJR
> >
> >>So where is a
> >> glue that holds a blocks/extents of a segment toegether ?
> >
> >There is no such substance.

>
> the data dictionary for dictionary managed tablespaces (uet/fet) and the
bitmap
> header for LMTs does this.

>
>


> >

> >
> >> - what is internal structure of a datafile ? I am not asking to know
the
> >(c)
> >> details but just a big picture. Once I did an append to one of a
datafiles
> >> with tar ...
> >>
> >> Please, point me to some reference on Oracle internals.
> >
> >Steve Adams has a book. O'Reilly, something like 'internal services for
> >Oracle'. Go to his web site (www.ixora.com.au) and you'll be able to see
it
> >(and its accurate title, which I've forgotten) under the 'Resources'
link).
> >

>
> I would say actually the Oracle concepts guide answers all of these
questions
> very elegantly.

> http://technet.oracle.com/doc/oracle8i_816/server.816/a76965/toc.htm

> these "internals" aren't really that internal.....

>


> >Regards

> >HJR

> >

> >

> >

> >>

> >> Just beeing courious,

> >> Andrej

> >>

> >>

> >
> >

>


> --

> Thomas Kyte (tkyte@us.oracle.com)             http://asktom.oracle.com/

> Expert one on one Oracle, programming techniques and solutions for Oracle.
> http://www.amazon.com/exec/obidos/ASIN/1861004826/
> Opinions are mine and do not necessarily reflect those of Oracle Corp
> Received on Sun Dec 09 2001 - 17:19:10 CST