Re: Instance question

"Chris O" <itoys1 -a t- optusnet -d o t- com -d o t- au> wrote in message news:<3f3cb704$0$14558$afc38c87_at_news.optusnet.com.au>...
> "Larry Lowe" <llowejr_at_usa.net> wrote in message
> news:ad17577.0308140714.1b14d778_at_posting.google.com...
> > I have a question about weather it is better to have multiple
> > instances on a system or multiple users in the database? Say we have
> > a development, testing and training copies of the schema. Is it
> > better to have 3 instances or one instance and 3 users?
> >
> > Thanks
> > Larry
>
> Hi Larry. Some responses [which we will ignore] aren't very helpful. I'll
> try to do a little better.
>
> The first point to note is that each Oracle instance requires a reasonable
> amount of system resouces as usually a considerable amount of memory is
> allocated to the instance and on UNIX there is typically half a dozen
> background processes hanging around just waiting to do your bidding. For
> this reason you would normally expect to keep the number of instances to a
> minimum.
>
> The second point to note is that each extra instance is going to increase
> the administration work load for the DBA and system admionistrators. We are
> not just talking about a directory or folder. Each instance must be
> started, backed up and checked to ensure all is well. The more instances
> you have the more work you have. For this reason also, you would normally
> expect to keep the number of instances to a minimum.
>
> With that said one has to address the issues of isolating developers from
> the production and acceptance databases [I'm using database interchangeably
> with instance]. This tends to demand separate databases for these at least.
> So what you have left is a desire to keep the number of databases (and thus
> instances) to a minimum and most likely a requirement to support a number of
> different environments. Typically it is desirable to isolate some
> developers from other developers. Depending on the way the database side of
> your applications are put together it may be quite simple to have multiple
> copies of the app installed in a single database. If your app is contained
> in a single schema and does not reference much outside it then this is
> likely to be the case. On the other hand, if your app is spread across half
> a dozen schemas and references all sorts of external things then you are
> going to have to work a lot harder to support multiple implementations of
> your app in the one database. Unfortunately, Oracle does not support any
> concept of specifying a catalog. Oracle supports a single global catalog
> and all schema names must be unique within this catalog. What this means is
> that if you have DDL scripts to create your applications schemas and your
> schemas reference objects in other schemas you will end up having to use a
> combination of [hopefully private] synonyms and a liberal sprinkling of
> lexical substitution variables in your DDL scripts. These lexical
> substitution variables [using the SQL*Plus terminology] allow you to specify
> the schema names when you build your schemas.
>
> If you are familiar whith Oracle schemas then this should be pretty evident.
> If not, then you have a lot of reading to do. If you can contain your
> application to a single schema, things will be pretty straight forward.
>
> As a final thought, I've seen some people recommending that each developer
> have their own personal database [typically on the own workstation]. This
> does avoid most of the issues above except for these two:
>
> 1. Every developer has to become a kind of mini DBA. I'm not sure what I
> think about this concept. I'm sure many people all have different opinions
> on this one. Ultimately, its success would depend on the level of expertise
> of your developers.
>
> 2. It most likely exacerbates the administration problem mentioned in point
> two above. Do your maths, If you have 15 developers each with their own
> Oracle database and you want to apply the latest upgrade....
>
>
> I hope this is some help.
>
> Cheers

Thanks Chris, that was helpful.

Larry Received on Fri Aug 15 2003 - 17:55:54 CEST