Re: Oracle internals.

In article <YrSQ7.11$bk2.1082_at_inet-nntp1.oracle.com>, "Howard says...
>
>
>"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.
>

ok picky picky -- you are right ;)

got me on that one, i translated segments into tables...... sorry...

>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
>>
>
>

--
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