Re: ALTER TABLE (schema migration)

A copy of this was sent to "Paul Gladden" <pgladden_at_lucent.com> (if that email address didn't require changing) On Wed, 17 Nov 1999 11:00:51 -0700, you wrote:

>We're moving to Oracle and I cannot find any information
>relating to Oracle's locking hierarchy for an "alter table"
>or how Oracle's "alter table" is facilitated.
>
>I need to know how the "alter table" occurs, whether the
>table is modified "in-place" or whether Oracle makes
>a table "copy" based on the schema change (add column, drop column, modify
>column) and then drops the source
>table.
>

all modifications except DROP are very very fast (in place).

set unused is the 'fast' way to drop a column (it flag deletes them). you would mark columns unused and schedule some down time to actually drop them and reclaim the space (or not)

>What are the conditions which trigger a "copy" migration? How can I detect
>these conditions so I can schedule them?
>
>Maybe Oracle migrates everything "in-place"....
>
>I'm trying to avoid a lengthy table level lock to a
>production system.
>
>Thanks in advance for any replies or pointers where I
>can locate this information.

--
See http://osi.oracle.com/~tkyte/ for my columns 'Digging-in to Oracle8i'... Current article is "Part I of V, Autonomous Transactions" updated June 21'st  

Thomas Kyte                   tkyte_at_us.oracle.com
Oracle Service Industries     Reston, VA   USA

Opinions are mine and do not necessarily reflect those of Oracle Corporation Received on Wed Nov 17 1999 - 15:34:58 CST