Oracle Concepts Question

[RK]

I was reading the Concepts manual and was puzzled by this sentence.
Can anyone elaborate on this:

<snipTables are the basic unit of data storage in an Oracle
database. Database tables hold all user-accessible data. Each table
has columns and rows. Oracle stores each row of a database table
containing data for less than 256 columns as one or more row
pieces.</snip>

What is this 256 column limit. I thought row chaining / migration
depended on row size.


See http://download-west.oracle.com/docs...ntro.htm#20658


Thanks

rajXesh

[Ron]

Re: Oracle Concepts Question



"When a table has more than 255 columns, rows that have data after the 255th
column are likely to be chained within the same block. This is called
intra-block chaining. A chained row's pieces are chained together using the
rowids of the pieces. With intra-block chaining, users receive all the data
in the same block. If the row fits in the block, users do not see an effect
in I/O performance, because no extra I/O operation is required to retrieve
the rest of the row."

Hope this answers the question.

Regards,

Ron

DBA Infopower

http://www.dbainfopower.com

Standard disclaimer:

http://www.dbainfopower.com/dbaip_advice_disclaimer.html

"RK" <rajXesh@hotmai l.comwrote in message
news:548b9514.0 402061242.64b4b 0dd@posting.goo gle.com...

I was reading the Concepts manual and was puzzled by this sentence.
Can anyone elaborate on this:
>
<snipTables are the basic unit of data storage in an Oracle
database. Database tables hold all user-accessible data. Each table
has columns and rows. Oracle stores each row of a database table
containing data for less than 256 columns as one or more row
pieces.</snip>
>
What is this 256 column limit. I thought row chaining / migration
depended on row size.
>
>
See

http://download-west.oracle.com/docs...ntro.htm#20658

>
>
Thanks
>
rajXesh

[RK]

Re: Oracle Concepts Question

Thanks, I found that paragraph on intra-block chaining in the Concepts manual.

-- rajXesh

"Ron" <support@dbainf opower.comwrote in message news:<PYKdneruv 9bzorjd4p2dnA@c omcast.com>...

"When a table has more than 255 columns, rows that have data after the 255th
column are likely to be chained within the same block. This is called
intra-block chaining. A chained row's pieces are chained together using the
rowids of the pieces. With intra-block chaining, users receive all the data
in the same block. If the row fits in the block, users do not see an effect
in I/O performance, because no extra I/O operation is required to retrieve
the rest of the row."
>
Hope this answers the question.
>
Regards,
>
Ron
>
DBA Infopower
>

http://www.dbainfopower.com

>
Standard disclaimer:

http://www.dbainfopower.com/dbaip_advice_disclaimer.html

>
>
>
"RK" <rajXesh@hotmai l.comwrote in message
news:548b9514.0 402061242.64b4b 0dd@posting.goo gle.com...

I was reading the Concepts manual and was puzzled by this sentence.
Can anyone elaborate on this:

<snipTables are the basic unit of data storage in an Oracle
database. Database tables hold all user-accessible data. Each table
has columns and rows. Oracle stores each row of a database table
containing data for less than 256 columns as one or more row
pieces.</snip>

What is this 256 column limit. I thought row chaining / migration
depended on row size.


See

http://download-west.oracle.com/docs...ntro.htm#20658

Thanks

rajXesh