Re: Sequences in OPS/RAC

Yes, I've been aware of the difference between ORDERED and CACHED.

However, the Builder.Com article quite explicity asserts "Sequence generator numbers are guaranteed to be unique only for a single instance, which is unsuitable for use as a primary key in parallel or remote environments, where a sequence in each environment might generate the same number and result in conflicts
Sequence generator numbers are guaranteed to be unique only for a single instance, which is unsuitable for use as a primary key in parallel or remote environments, where a sequence in each environment might generate the same number and result in conflicts"

As Tim has pointed out earlier, the author of the article might have confused uniqueness with ordering.
{I've sent copies of the builder.com article by seperate emails to Raj and Tim}

Hemant

At 07:59 AM 03-11-03 -0800, you wrote:
>In the "Oracle9i Real Application Clusters Administration" manual, there
>is a chapter
>about sequence numbers generator. Before believing to the snake oil
>sellers, read
>the fine manual. Sequence numbers are guaranteed to be unique PER
>DATABASE. What they're
>not guaranteed is to come in ordered fashion. When sequence number are
>cached (that is the
>default), they're cached separately, for each instance. Each instance
>returns the contents
>of its cache, so it is possible for the smaller number being returned
>after a larger one.
>There is "ORDERED" flag to deal with that, but that can be extremely
>expensive and impose
>significant overhead on your cluster.
>
>On 11/03/2003 10:39:26 AM, Hemant K Chitale wrote:
> >
> >
> > I have always been comfortable with the idea that Sequences continue to
> > guarantee
> > uniqueness even in OPS / RAC environments.
> >
> > However, a recent Builder.Com article by Scott Stephens on the SYS_GUID
> > function has these lines :
> > "Sequence generator numbers are guaranteed to be unique only for a single
> > instance, which is unsuitable for use as a primary key in parallel or
> > remote environments, where a sequence in each environment might generate
> > the same number and result in conflicts. An identifier created by SYS_GUID
> > is guaranteed to be unique for each database."
> >
> > Huh ?! Do the lines mean that a single sequence can have duplicate values
> > in the two instances of an RAC cluster ?
> >
> >
> > Hemant K Chitale
> > Oracle 9i Database Administrator Certified Professional
> > My personal web site is : http://hkchital.tripod.com
> >
> >
> > --
> > Please see the official ORACLE-L FAQ: http://www.orafaq.net
> > --
> > Author: Hemant K Chitale
> > INET: hkchital_at_singnet.com.sg
> >
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>
>Mladen Gogala
>Oracle DBA
>
>
>
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Hemant K Chitale
Oracle 9i Database Administrator Certified Professional My personal web site is : http://hkchital.tripod.com

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Hemant K Chitale
  INET: hkchital_at_singnet.com.sg

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