Re: Question about concurrency?

In article <360B4400.6FF887AA_at_slagehs.dk>,   Rene Rydell <dm2121_at_slagehs.dk> wrote:
> Hello
>
> we are making an assignment in our school about large databases and
> their concurrency systems and recovery systems.
>
> And I was was hoping some of you guys could help us out, and
> mayby explain to us what kind concurrency techniques Oracle uses.
> And maybe recovery systems if any.
>
> Thanks in advance.
>
> Rene Rydell
>
>

Contact Oracle directly for more details but just a couple points.

CONCURENCY Oracle uses a technique called multiversioning. This allows a query to read many records of the database while they are being updated. The net effect is less contention for locks and thus faster performance. The cost is more disc space/memory for long running queries.

RECOVERY Oracle mantains REDO logs for every transaction. If the system comes down unexpectedly, the startup handles recovery by applying the transactions in the REDO logs and rolling back any that were not committed.

That is a very high level summary. There are other features of concurrency and recovery that I left out. (I don't have my research handy, but I can look this up again, if you ask.)

Some of the ORACLE manuals, especially the Server and DBA manuals contain much more information and explaination. The last time I researched this, only one other database used multiversioning, INTERBASE from INPRISE(formerly BORLAND). IMHO, multiversioning is the best approach to concurrency. It is not without problems, but in the main performs better than other methods.

Good luck in your research.

--
Ed Prochak
Magic Interface, Ltd.
440-498-3702

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