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Connor McDonald

Thanks for the question, Ali.

Asked: May 13, 2018 - 6:44 am UTC

Last updated: May 21, 2018 - 11:38 am UTC

Version: 12c

Viewed 1000+ times

You Asked

if we have multiple datafiles of 32GB and there are fully utilized.

Can chained and migrated rows occurs due to the maximum datafile utilization?

and Connor said...

Nope. Chained and migrated rows are only due to *rows* being "too large", where too large could be:

- more than 255 columns
- regularly updating rows that were initially small in size and are now larger than pctfree will allow
- just really big rows (eg lots of varchar2(4000) columns all filled with data)

The only issue with full datafiles is making sure you always have sufficient free space for your database to grow so users do not get errors.

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Comments

Logical Storage Structures\ Chained and Migrated rows & (ASSM)

Ali Al Hajri, May 14, 2018 - 4:26 am UTC

Thank you so much Connor McDonald for the quick response.

if the database is configured by Automatic Segment Space Management method, will the table get impacted by Chained and migrated rows, if the below point is present?

*The row is too large as in it has more than 255 columns.

Connor McDonald
May 18, 2018 - 2:08 am UTC

We can only fit 255 columns in a block. Some good reading here

https://jonathanlewis.wordpress.com/2015/02/19/255-columns/
https://jonathanlewis.wordpress.com/2017/05/19/255-columns-2/
https://jonathanlewis.wordpress.com/2017/05/23/255-again/
https://jonathanlewis.wordpress.com/2018/02/28/255-columns-3/

Logical Storage Structures\ Chained and Migrated rows & (ASSM)

Ali Al Hajri, May 20, 2018 - 4:54 am UTC


Connor McDonald
May 21, 2018 - 11:38 am UTC

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