Re: In praise of auto space management

Andrew Mobbs wrote:
>
> Given my repeated denouncements of UNDO tablespaces here recently, I
> thought that I should balance this by singing the praises of automatic
> segment space management.
>
> It's wonderful. Use it. Wave goodbye to headaches of worrying about
> balancing freelists and freelist groups, ensuring you've enough on all
> the segments, banging your head against a wall as you discover you've
> missed freelist groups off a vital but obscure segment.
>
> I've tested up to 96 parallel batch processes on a 32 CPU machine,
> inserting a sustained rate of well over 10000 rows per second into a
> single table. No buffer busy waits, in fact, no problem at all.
>
> Thank you, Oracle development.
>
> --
> Andrew Mobbs - http://www.chiark.greenend.org.uk/~andrewm/

This this experiment...

create table REALLY_SMALL as select * from dual;

then issue

select * from REALLY_SMALL

takes 3 logical IO's in an LMT.
takes 7 (!!!) logical IO's in an auto-seg-space LMT

Not a criticism on seg-space-mgt really (it only takes 1 IO if the table is an IOT)...but one to be wary of.

I've also seem other comments along the lines of the bitmap blocks possibly taking up a lot of space in the buffer cache, but I cannot comment on that hypothesis.

Cheers
connor

-- 
==============================
Connor McDonald

http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue..."