Re: Oracle vs SQl Server

In article <3A4EE07F.F4609514_at_someone.edu>,   Some Body <somebody_at_someone.edu> wrote:
> I have a basic question with regards this comparison:
>
> What are the relative disk-space requirements for the program files
 and
> the data? I'm guessing that Oracle needs at least twice the disk
 space
> for the data, because of the need to hold the redo logs, archive logs
> and also the need to preallocate space not yet needed for data. SQL
> Server, I believe, gets more disk space as needed from the OS. Is
 this
> correct?
>

Not completely.

The redo logs, archive logs do take up more space. The archive can be shut off. The redo logs are part of the main feature of Oracle. They provide the mechanism for allowing all readers to continue reading data even when someone is writing to the same area. It is possible to restrict this area, but at some cost. When running on a bigger system -- the idea of using 200M - 1G of space for redo logs is not terribly significant. There are also other areas like SYSTEM, TOOLS, TEMP and USER -- default tablespaces used for a variety of purposes.

Similarly Oracle trys to grab some of the memory. I have two instances each using about 1.8G of RAM. Not a lot relative the overall available space -- 12G in this case.

As to the size of data storage, it is possible to either preallocate or allow the system to expand as is needed. Generally one want to have within 20% of the actual data. Oracle will slow down ( Had this happen to me when the initial load was 10% of the space ) if too much free space is present in any give tablespace. Tablespaces are designed by the user to grow at a specific rate. The amount is generally a lot bigger than the next row. Within the tablespace -- data is allocated via extents, a subdivision of the tablespace.

As to using twice the space, it has alot to do with the amount of data. When one is working with 2-5Tbytes of data, the system areas (redo, system, etc) are not really significant. I just finished setting up a database -- I would estimate that the system is using 2-3G when all the tablespaces are expanded to their limits.

If you are trying to get Oracle to run on a small machine -- it can be done. I had a system that ran in 3G, 500M for the system, 2.5G for data.

As to a comparison, I am not sure what the issue is. Without redo logs, you are really in a quandry. Dynamically allocating all disk usage at runtime is expensive. Even on laptops, the idea of having 30-60G is not unexpected. Storage volume is generally not a concern of most developers.

--
Michael Krolewski
Rosetta Inpharmatics
mkrolewski_at_rii.com
              Usual disclaimers


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