Re: "Correct" term for a 1:1 relationship between a "database" and an "instance" where > 1 such things are on the same physical server?

From: dana <>
Date: Wed, 22 Jul 2009 06:37:31 -0700 (PDT)
Message-ID: <>

Thanks Mark. That was helpful. You wrote:

> In most practical uses you can use the term database to refer to both the physical database and the instance.

> database: Collection of data that is treated as a unit. The purpose of
> a database is to store and retrieve related information. Each Oracle
> database instance accesses only one database.

So when people loosely use the term "instance" or "database instance" they're not completely off base, are they? If each instance can ever only access one, and only one, database, then it shouldn't be "considered harmful" to speak this way? Or is the definition implying that a particular instance can only access one and only one database at any one time? I think this was what Tom Kyte was saying in the rest of that book section. I need to re-read it, and will.

Here's another question for you:

  1. Would there ever be any practical reason for two instances (procs + SGA) to access the same database (collection of data treated as a unit) on the same, unpartitioned physical server?
  2. Tangentially related, while I'm at it--is the chief and most obvious benefit of RAC High Availability? Are claims that RAC can be used for scalability mostly hype? Last I checked, there was controversy over this one--guess I need to re-read the "Why You Don't Need RAC" article; never used RAC and I'm not sure I can even articulate precisely what it does let alone how it does it. How does RAC relate to the concepts of "instance" and "database"?

> instance: A system global area (SGA) and the Oracle Database
> background processes constitute an Oracle database instance. Every
> time a database is started, a system global area is allocated and
> Oracle Database background processes are started. The SGA is
> deallocated when the instance shuts down.

> Notice the use of the term Oracle database instance appears in both definitions.


Dana Received on Wed Jul 22 2009 - 08:37:31 CDT

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