Ok... No flame war...

>>who come from an Informix background like me, but also know Oracle.

I do. 15yrs informix, couple on oracle... And been to the classes too.
Still tend to avoid it as much as possible(oracle), but just found out
yesterday I might not have the luxury to do that much longer. If you go
to sqlserver classes, you may find that is easier to understand, I did.
Altho sqlserver is GUI up the wazoo, the logic of it is much more like
informix (and therefore DB2 I have heard) whereas oracle is in a class
by itself.

>>I think the specialise in their specific course, and the Fundamentals
guy couldn't answer my performance tuning questions.

I would also suggest you take oracle classes from oracle. I was
disappointed with the 3rd party vendor teaching in this area. That is
not to say the oracle teachers aren't all that "in depth" either. I
have been to enough oracle training classes to say with some confidence
that they will pitch a lot of classes to you during your class.... Seems
for every "feature" there is a least a 2 or 3 day class explaining it.
Oracle does not offer an internals class for anything. Perhaps ya'll
should take advantage of IBM's informix internals while it still
exists....

>>One of my biggest questions - why does every Oracle dba I speak to,
say that fragmentation of tables / too many extents (non-contiguous
space) does not matter. Surely that should still matter, no matter which
database you use ?

It matters to some degree on oracle. But the one feature about oracle
that I do understand and have actually come to respect is that it
automatically releases extents if they are not used... Thereby allowing
other tables in that tablespace to take that space, whereas with
informix you have to thump it on the head (reorg) to get a table to drop
extents. This is a feature I have whined about quite a bit lately and
altho I have no direct support from informix (mine comes via SAP),
Jonathan Leffler graciously picked up my request and added it to the
feature request list for IBM... So that may be coming to informix in
perhaps release 9.6 but don't hold me or JL to that.
We have SAP R3 on informix (1.3TB) and SAP BW (business warehouse) on
oracle. My boss (longtime Oracle DBA) says it is nice to keep oracle
under 1000 extents... When it gets that obnoxious, then reorg, but
otherwise since oracle auto-releases... No point to reorg for extent
management. I believe SQLServer behaves like oracle on this issue (but
a bit foggy on that detail).
So, yes, regarding oracle and extent management, you may look forward to
relaxing your guard a bit on that.

>>Another big question - why does Oracle say that cooked space should be
used rather than raw space - and this answer I got from their
performance tuning guy as well.

Dude, oracle doesn't care about performance........
Oh yeah... No flaming here ...

I believe it is because oracle was not developed with it (is oracle
older than informix or as I sometimes think, informix especially on
unix, is older than oracle?)... Back in the day when the o/s definitely
dragged the DB's ability to access data, informix went directly to the
disk. Oracle didn't bother.... And in some ways with all the built in
cache for disk management, server management, DB management.... Oracle
still doesn't see the validity of putting that much effort into
perfection.
You may also find yourself getting very frustrated with ora-600 errors
(these happen when the DB gets confused and can't deal with something
.... Ora-600 is very generic, mostly I ignore them... I see my oracle
DBA counterparts (with much more experience than i) do the same... If
the DB doesn't come down... Then it's ok).
Perfection is not oracle's game.

You may also want to keep in mind that while it might be pretty standard
for informix DBAs to allocate space in 2 GB chunks (or bigger if you
turned that feature on)....
It is perhaps not the best idea to do that on oracle.
1) if you allocate a big chunk (data file) on oracle, you will wait
patiently while oracle null-fills (or something) the entire large size
you chose. It seems more oracle DBAs prefer to allocate small datafiles
and let them auto-grow... Thus the initial addition of the datafile is
fast.
2) another reason you may want to go with small datafiles initially
rather than any 'standard' 2GB chunk you may have grown accustomed to is
that with oracle you can SHRINK the datafile. That's one easy way to
decrease the size of your DB if you have perhaps archived data or moved
data or whatever. So, for example, if you had 5 datafiles in one
tablespace and for some reason moved/archived most of the data there....
You could drop all empty datafiles, and shrink the remaining one to it's
original allocated space (so if you gave it 2GB to begin with, you can
not shrink down to 100MB, but if you originally allocated it as 100MB
and it auto-grew to 2GB, then you have the possibility to shrink the
datafile back down to 100MB if you have moved/dropped/etc the data in
that space).

Thanks,
NJ





-----Original Message-----
From: owner-informix-list@iiug.org [mailtowner-informix-list@iiug.org]
On Behalf Of Dirk Moolman
Sent: Wednesday, December 15, 2004 1:48 AM
To: informix-list@iiug.org
Subject: FW: Oracle ?


I just wanted to find a couple of people who come from an Informix
background like me, but also know Oracle. I just completed the Oracle
Fundamentals I course, but still have some questions that the instructor
couldn't answer.

I think the specialise in their specific course, and the Fundamentals
guy couldn't answer my performance tuning questions.

One of my biggest questions - why does every Oracle dba I speak to, say
that fragmentation of tables / too many extents (non-contiguous space)
does not matter. Surely that should still matter, no matter which
database you use ?

Another big question - why does Oracle say that cooked space should be
used rather than raw space - and this answer I got from their
performance tuning guy as well.

Dirk

-----Original Message-----
From: Art S. Kagel [mailto:KAGEL@bloomberg.net]
Sent: Tuesday, December 14, 2004 5:34 PM
To: Dirk Moolman
Subject: Re: Oracle ?

Dirk Moolman wrote:
> Is there anyone on this group that also works with Oracle ?

A little, but no recently. But there are others. What's up?

Art S. Kagel

> Dirk Moolman
> Database and Unix Administrator
> MXGROUP

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