Oracle FAQ Your Portal to the Oracle Knowledge Grid

Home -> Community -> Usenet -> c.d.o.server -> Re: clustering and high availability?

Re: clustering and high availability?

From: Daniel Morgan <>
Date: Thu, 10 Jun 2004 21:29:06 -0700
Message-ID: <1086928161.576330@yasure>

Howard J. Rogers wrote:

> "Daniel Morgan" <> wrote in message
> news:1086914524.786060_at_yasure...

>>Serge Rielau wrote:
>>>I thought RAC is shared disk, not shared everything.
>>You thought wrong. Oracle has had a shared everything architecture
>>for a very long time.
>>Anytime you want to see 8 separate instances on 8 separate nodes
>>simultaneously write to a single datafile come to Seattle.

> Shared *everything*??
> So node 1 is able to directly access and write to node 2's RAM?
> Or node 7 is able to process instructions on node 4's CPU?
> Cache fusion might be clever, but it's not *that* clever!
> The usual definition of "shared everything" in clustering circles is
> something along the lines of "In the shared-everything cluster model, all
> servers or cluster nodes in the cluster are given equal to the shared
> resources". Now, even granted that we are talking Oracle software here, and
> not physical hardware, the 'shared resources' in a RAC are, and are only,
> the database files. Not, for example, the instances. The instance on Node 1
> cannot directly access and write to buffers in Node 2's buffer cache, but
> has to ask politely for the data to be shipped to it so that it can work on
> it 'locally'.
> Therefore, Serge is I think correct to define carefully that RAC means
> shared disk storage, or shared database files, not actually shared
> "everything". Ordinarily, it would be a bit of a joke and technical
> shorthand, of course. But since Oracle decided to make up and sell RAC on
> the basis of the 'cache fusion' marketing hype, which does indeed suggest to
> the unwary that, somehow, instances really are 'merged' or 'fused' across
> nodes, I think Serge's point is actually not a bad one to make now and
> again.
> Regards
The phrase "Shared everything" has been very well defined by Oracle for many years. And as I know you are an expert I also know you know this without me having to tell you ... Something you clearly indicate in your response. And we both know you could have made mention of block sharing rather than RAM sharing but chose not to: Why?

And even you Howard clearly read that the subject was related to disk. Neither Serge nor I said a single thing about memory. So you are, in my far less than humble opinion, trying to start something.

If you are looking for an argument ... look elsewhere. I'll not play that game.

Daniel Morgan
(replace 'x' with a 'u' to reply)
Received on Thu Jun 10 2004 - 23:29:06 CDT

Original text of this message