Re: Article about supposed "murky" future for Oracle

From: Daniel Morgan <damorgan_at_x.washington.edu>
Date: Wed, 31 Mar 2004 21:53:55 -0800
Message-ID: <1080798815.100054@yasure>

Stu Charlton wrote:

> "Noons" <wizofoz2k_at_yahoo.com.au> wrote in message news:<406ab360$0$15064$afc38c87_at_news.optusnet.com.au>...
>
>

>>No.  Incorrect.  And completely ignoring the reality of data processing.
>>Versioning has NOTHING to do with isolation levels and it
>>solves the problem in a TRANSPARENT fashion.

>
>
> I agreed with you up until this one, sorry. There are some subtle
> aspects to Oracle's versioning mechanism that makes its SERIALIZABLE
> isolation level unlike other databases' SERIALIZABLE isolation levels,
> so it is most definitely *NOT* transparent.
>
> This is not because Oracle is deficient; it is because ANSI SQL's
> isolation definitions are ambiguous and inadequate. Oracle's
> SERIALIAZBLE level is different in that it makes a "non-serial"
> history possible (this is called "write skew" , i.e. Tom Kyte's
> example in his expert one-on-one book). This usually is an "OK" thing
> in practise as long as you're aware of it; the benefits outweigh this
> anomaly usually. A form of phantom write is also sometimes possible.
>
> This paper is a short and very readable explanation of the problem &
> how Oracle fits in with its Snapshot Isolation...
>
> http://www.cs.duke.edu/~junyang/courses/cps216-2003-spring/papers/berenson-etal-1995.pdf
>
> Cheers
> Stu

Thanks for the link to the paper.

-- 
Daniel Morgan
http://www.outreach.washington.edu/ext/certificates/oad/oad_crs.asp
http://www.outreach.washington.edu/ext/certificates/aoa/aoa_crs.asp
damorgan_at_x.washington.edu
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Received on Wed Mar 31 2004 - 23:53:55 CST