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: Mark D Powell <>
Date: Wed, 22 Jul 2009 06:17:58 -0700 (PDT)
Message-ID: <>

On Jul 22, 8:24 am, dana <> wrote:
> What is the "correct" term for a 1:1 relationship between a "database"
> and an "instance" where there are at least two such "things" on the
> same physical server?
> Nearly all the Oracle docs and books define a database something like
> the following:
> DATABASE - a collection of datafiles and oracle config files; useless
> without an "instance" to access the database.
> INSTANCE - a collection of background procs and memory structures,
> used to access a "database."
> Where I work, people typically call each "thing" mentioned in my
> Subject: line an "instance" or a "database instance." What is the
> "correct" term for having more than one of these "things" on the same,
> unpartitioned physical server?
> This may be splitting hairs; but when people don't or can't come to
> terms, confusion ensues--and that's typically a Bad Thing.
> I noticed, or rather a colleague of mine did, that even Tom Kyte mixes
> terms. In the book Expert Oracle Database Architecture (2005 edition)
> on page 50, in the bullet-pointed definitional paragraph for Instance,
> he throws the word "database instance" into the mix. A "no no"
> according to my colleague (don't shoot the messenger, please); because
> the vernacular seems to be "instance" or "database instance" for the
> each "thing."
> I like to be precise with terms, but then there are business
> stakeholders who use technically imprecise terms; even DBAs seem to
> make this mistake.
> Would it be less confusing to all concerned simply refer to an "Oracle
> SID" to indicate a 1:1 pairing of an "instance" and a "database" where
> there are 2 or more of these "things" on a single, unpartitioned
> server?
> Help! I want to "get it right" without being pedantic and trying to
> educate every last stakeholder in a large organization. Maybe
> education is the "right" thing to do, but when even DBAs use the term
> "instance" incorrectly... well, that might not end well. :-)
> Dana

In most practical uses you can use the term database to refer to both the physical database and the instance. The term instance is short for database instance which is just a way of specifying the instance for a specific database when you need to make a distinction

From 11g Glossary

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.

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.

HTH -- Mark D Powell -- Received on Wed Jul 22 2009 - 08:17:58 CDT

Original text of this message