Rick Denoire <100.17706_at_germanynet.de> schreef in berichtnieuws
e3319vg58ngj27fk8t4uaji6l94bh5av72_at_4ax.com...
| "Anton Buijs" <aammbuijs_at_xs4all.nl> wrote:
| One of the most popular "hobbies" of the developers is to add new
| column to existing tables and to populate these using update. Don't
| you think that - assuming the blocks have no more space free for the
| longer rows - this would cause ALL blocks to become migrated? In
| consequence, every input request for one record would cause 2 read
| operations, so making things 100% slower...
|
| Don't know how to avoid this. One can't just set PCTFREE to 40% for
| every table, just in case one developer decides to add one column with
| large fields.
|
| Bye
| Rick Denoire
Increasing pctfree would cause waste of space. You can't avoid many migrated
rows when columns are added, I agree. So once in a while you need to reorg
such tables, not very frequently, but it can be necessary now or then.
There is a performance penalty but I won't say it gets 100% slower. Maybe
the 2nd block was necessary too, to read the other rows matching the query,
it could be read anyway by the OS or because of the Oracle settings
(multiblock reads), required by another query. The total picture is always
much more complex than looking at 1 session.
Received on Sun Apr 06 2003 - 15:57:40 CDT
