Re: About rollback consumption

Hi Jonathan,

I'm not sure we disagree (or that I was wrong!).

I posted earlier that two *concurrent* or pending transactions couldn't share the same block (at least, that's what I was *trying* to post!)

Your listing here shows you doing a transaction, committing, and then doing a *second* transaction.

I'm not surprised you've re-used the one block, since your first transaction isn't reserving it -because you've just finished it with that commit.

Let me know if I'm missing something.

Regards
HJR

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"Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message
news:970145689.20485.0.nnrp-07.9e984b29_at_news.demon.co.uk...


>

> Howard,

>

> Your comments about rollback block usage aren't

> correct (at least in 8.1.5), although it is possible

> to produce experiments that make them look correct.

>

> Consider the following screen dump - which I contrived

> by reducing a database to having a single non-system

> rollback segment.  The camera did not cut away whilst

> this screen dump was going on ...

>

>

> SQL> insert into junk values (1);

>

> 1 row created.

>

> SQL> select start_ubafil, start_ubablk, start_ubarec from v$transaction;

>

> START_UBAFIL START_UBABLK START_UBAREC

> ------------ ------------ ------------

>            3          116           16

>

> SQL> commit;

>

> Commit complete.

>

> SQL> insert into junk values (1);

>

> 1 row created.

>

> SQL> select start_ubafil, start_ubablk, start_ubarec from v$transaction;

>

> START_UBAFIL START_UBABLK START_UBAREC

> ------------ ------------ ------------

>            3          116           17

>

> SQL> commit;

>

> Commit complete.

>

>

> As you can see, there are likely to be multiple

> rollback records available within a rollback block,

> and it is possible for one transaction to end leaving

> space in a rollback block that another transaction

> can acquire.  I have two consecutive transactions

> which have used the same rollback block.

>

> However, you may find that two processes cannot use

> the same rollback block simultaneously (I haven't

> actually checked that in 8.1 - it used to be true),

> and block usage in rollback segments always moves

> on, so if you tried to repeat the test on a system where

> there were always twice as many active transactions

> as rollback segments, then you would get results

> that suggested that any transaction had to use a

> whole rollback block.

>

>

> --

>

> Jonathan Lewis

> Yet another Oracle-related web site:  http://www.jlcomp.demon.co.uk

>

> Howard J. Rogers wrote in message <39d324af$1_at_news.iprimus.com.au>...

>

> >>   INSERT (?)

> >>   DELETE (?)

> >>   UPDATE (?)

> >>

> >> I write them in a supposed growing consumption order. Can anyone

 confirm


> >> that ?

> >>

> >

> >Also not true.  A rollback block stores the prior image of the data.  The

> >before image of an insert is the rowid where the insert is to take place.

> >Which is trivial in size -but it would still require an entire rollback

> >block.

> >

>

>

>