Oracle Concepts Question

[RK]

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

<snip> Tables 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]

"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

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"RK" <ra*****@hotmail.com> wrote in message
news:54**************************@posting.google.c om...

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

<snip> Tables 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]

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

-- rajXesh

"Ron" <su*****@dbainfopower.com> wrote in message news:<PY********************@comcast.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_ad...isclaimer.html

"RK" <ra*****@hotmail.com> wrote in message
news:54**************************@posting.google.c om...

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

<snip> Tables 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