Re: question about rollback and redo

From: Stan <stan0074_at_remove_this.comcast.net>
Date: Sat, 20 Sep 2003 21:44:02 GMT
Message-ID: <3F6CCA22.20803@remove_this.comcast.net>

Jonathan Lewis wrote:
> (assuming no indexes)
> When you delete a row the row plus about 80
> bytes of overhead gets put into the undo. A
> few bytes of change are made to the data block
> (deleted flag, ITL entry).
>
> The redo then contains a record consisting of
> two change vectors - each with an overhead
> of about 80 bytes. One change vector describes
> the change to the data block, and the other change
> vector describes the change to the redo block,
> which include the detail of the deleted row.

Just for clarification, you meant by undo block and not redo block on the 2nd change vector do you.

>
> Delete 1MB as 10,000 rows of 100 bytes, and
> you have 10,000 undo records - which is the
> 10,000 rows with 10,000 overheads - and
> 10,000 redo records which is 10,000 copies
> of the row plus about 20,000 lots of overhead.
>
> --
> Regards
>
> Jonathan Lewis
> http://www.jlcomp.demon.co.uk
>
> The educated person is not the person
> who can answer the questions, but the
> person who can question the answers -- T. Schick Jr
>
>
> One-day tutorials:
> http://www.jlcomp.demon.co.uk/tutorial.html
>
> ____Finland__September 22nd - 24th
> ____Norway___September 25th - 26th
> ____UK_______December (UKOUG conference)
>
> Three-day seminar:
> see http://www.jlcomp.demon.co.uk/seminar.html
> ____USA__October
> ____UK___November
>
>
> The Co-operative Oracle Users' FAQ
> http://www.jlcomp.demon.co.uk/faq/ind_faq.html
>
>
> "Ryan Gaffuri" <rgaffuri_at_cox.net> wrote in message
> news:1efdad5b.0309191139.5eab5f6d_at_posting.google.com...
>

>>Documentation isnt too clear on this(or Im just not following it).
>>
>>When you do a delete the entire row is copied to the rollback

>
> segment.
>

>>Now if Im deleting 1MB worth of data in the datafile(lets assume

>
> there
>

>>is no pctfree or pct used, just data), will 1MB of data be written

>
> to
>

>>rollback? Im assuming there will be less due to block header,

>
> etc...,
>

>>but how much less?
>>
>>Now when the rollback is written to redo, how much data does that
>>entail? What goes in a 'change vector'? Does the entire row get

>
> copied
>

>>twice? Once to the rollback and once to the redo logs?

>
>
>

-- 
-Stan

To reply remove the obvious ones from my email address

Received on Sat Sep 20 2003 - 16:44:02 CDT