LMT and DMT

From: Norman Dunbar <Norman.Dunbar_at_lfs.co.uk>
Date: Wed, 5 Feb 2003 10:25:25 -0000
Message-ID: <E2F6A70FE45242488C865C3BC1245DA70343DAF9@lnewton.leeds.lfs.co.uk>

Morning Tingl,

Hmmm - comments inline !

Cheers,
Norman.

Norman Dunbar
Database/Unix administrator
Lynx Financial Systems Ltd.
mailto:Norman.Dunbar_at_LFS.co.uk

Tel: 0113 289 6265
Fax: 0113 289 3146
URL: http://www.Lynx-FS.com
-------------------------------------

-----Original Message-----
From: tingl [mailto:one4all_at_all4one.not] Posted At: Wednesday, February 05, 2003 1:33 AM Posted To: server
Conversation: LMT and DMT
Subject: Re: LMT and DMT

>> DMT gives you more options when it comes to extent sizes in a single
>> tablespace.

This is indeed true, DMTs allow anyone with create table privs to create totally random extent sizes that are of no use to any other object in the same tablespace. Once an extent is dropped and bits of it are used for other objects, then you get free space fragmentation. Having FSF leads to the problem where a tablespace has, say 100 MB free, but as it is all in randon sized chunks, the biggest of which is about, say 2 Mb, then trying to allocate an extent for one ofg your many different extent sizes will fail if the size required is bigger than the afore mentioned 2 Mb.

Not only that, but any import into this tablespace can totally screw things up if the exporter has used COMPRESS=YES (the default) - this is a sure fire way to run out of space half way through an import - I know because I have a customer who insists that one extent is good and leads to much improved performance.

<SNIP>
>> In the time we will continue to use DMT until we have to make a
choice between uniform LMT - the one-size-fit-all
>> approach or system LMT - the brain dead approach. :)

Personally, LMT's have been the best thing to hit Oracle databases since the last best thing - they make life so much easier, and even our users notice a performance increase.

Anyway, if you don't want to have 'one size fits all' then simply create a couple of other tablespace with their own 'one size' and remember, if you ask for initial of 2 Gb in a 64 Kb extent, you'll still get 2 Gb so where's the problem ?

Even better, if you have 100 Mb free in an LMT then you can use it all even if it is spread all over the place - no such thing as FSF anymore - I love it.

Cheers,
Norman. Received on Wed Feb 05 2003 - 04:25:25 CST