Re: Datafile size - Is bigger better?
- From: "JayDBA" <jaykash@xxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 15 Nov 2006 13:33:48 -0600
Excellent inputs from Jared, Wolfgang, Bob, Stephen and Richard.
Thanks for pointing out the rman backup details, I just did not think about it
and it totally makes sense. Glad to know that you are in favor of 2+ GB files
as I am. As for load balancing you are right, SAN/ NAS/ Raid I think take
pretty good care of load balancing and conceptually (conceptually only) I think
if it were not for the OFA we can pretty much live with putting all files on
one single Unix mount (list - feel free to shoot me down on this one :-))
My apologies to not have provided more details. Ours is a data warehouse
environment on a 64-bit O/S and we have multiple data warehouses/ marts that
run into 100's of GB to a few TB in size. Some tables alone are more than 50 GB
in size and larger ones can run into a couple of hundred GB. I am not working
as a dba in the current shop so dont have access to a lot of information that
can help; however being a dba for more than 8 years it just doesnt seem right
to me to have a 2gb limitation on the file size, especially on a VLDB
environment and I am trying to question myself for why "many small files" are
not good for a VLDB. I am on the same page as you are to set a max-limit on
the file size and precreate the datafile with the max size - keeps the mount
points from blowing up.
Excellent input and the example by Wolfgang; Thanks for reminding me of the
fact that the df header only takes up about 64K space. I now remember doing
that in my earlier shop about 3 years back. In fact I had created a sql script
that generated the "alter database .. resize" for all the files that had space
wasted due to this fact and it made reusable more than 125 GB of space across
different databases that spanned 3TB in size.
What can be the Query/ DML performance impact of having many smaller files in a
database? One of the things, I can come up with is:
1. Possibly slower checkpoints since CKPT has to work more to update many
smaller files.
Any more?
Regards.
------------------------------------------------------------------------------
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of JayDBA
Sent: Tuesday, November 14, 2006 5:57 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Datafile size - Is bigger better?
Can I trigger a discussion on the pros and cons of datafile max-size. I am in
a shop where the datafile size is limited to 2gb on a 64-bit platform (Raided)
and I am trying to weigh the pros and cons of having a larger file limit.
Pros:
1. Quicker recovery
2. Easy to load balance
Cons:
1. How often do we have to recover?
2. Is load balancing on the database level really an option for raided systems
3. On locally managed files, we loose header space equal to the extent size.
E.g. on a datafile with uniform extent sizing of 128M a 2gb file would waste 6%
space / file. This number can run into gigabytes on systems with 100's of
1000's of files
4. CKPT having to work more since it has to update many more smaller files.
Regards
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