Re: Database that spans over multiple computers

Hi Dino: have you ever tried to open a database in one session, forgetting that you've already got it open in another? If so, you might be familiar with the error message that runs something like 'Cannot mount database in exclusive mode'.

Those words are carefully chosen... you're trying to MOUNT the database, so clearly it's the controlfile that's just thrown the wobbly (and MAXINSTANCES is a parameter, like maxdatafiles, maxloghistory etc, that affects the internal structures of the controlfile). If MAXINSTANCES is 1 (the default), then only one Instance can open the Controlfile at a time (ie, exclusively).

In Parallel Server, as you clearly know already, multiple Instances can acquire the one Controlfile (and hence access all other files) -up to the limit specified by that parameter. So, multiple Instance, one database. As to that database being on multiple machines, well... you would normally create a shared storage array that the multiple machines can access. In that sense, the one database is shared across multiple boxes. (Although I think it might be more technically accurate to describe it as a single storage array mounted by multiple machines).

As to your other question about different kinds of services, I believe (but don't quote me) that has to do with accessing non-Oracle databases.

Regards
HJR

--
=============================!!=============================
The views expressed are my own only, and definitely NOT those of Oracle
Corporation
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"Dino Hsu" <dino1_nospam_at_ms1.hinet.net> wrote in message
news:buujgtkhgvqg6rlj0586fddq5bsntv6jq4_at_4ax.com...


> On Mon, 21 May 2001 22:04:43 -0700, "Daniel A. Morgan"

> <dmorgan_at_exesolutions.com> wrote:

>

> >Dino Hsu wrote:

> >

> >> Dear all,

> >>

> >> In a help page about Databse Identification by Service Name, it

> >> explains the reason why service name is used instead of SID (Oracle

> >> System Identifier) is that the former doesn't distinguish services

> >> from instances (an SGA, thus instance, was also identified by an SID).

> >> This implies that a database can provide multiple (different kinds

> >> of?) services to the clients within the same instance. Can anyone give

> >> a real example about this?

> >>

> >> It continues with this:

> >> "In Oracle 8i, a new naming schema has been implemented. Because a

> >> database can span multiple computers, both the service as a whole and

> >> each of its instances are specified."

> >> Why can a database span multiple computers, this really beats me.

> >>

> >> Any comments? Thanks in advance.

> >>

> >> Dino

> >

> >Take a close look at the following CREATE DATABASE command. It includes

> >the following parameter.

> >

> >CREATE DATABASE orabase

> >CONTROLFILE REUSE

> >LOGFILE  GROUP 1 ('/oramnt/u02/oradata/boris/oralogG1A.ora',

> >                  '/oramnt/u02/oradata/boris/oralogG1B.ora') size 3M

> >reuse,

> >         GROUP 2 ('/oramnt/u07/oradata/boris/oralogG2A.ora',

> >                  '/oramnt/u07/oradata/boris/oralogG2B.ora') size 3M

 reuse


> >

> >DATAFILE '/oramnt/u02/oradata/boris/system01.dbf'

> >   SIZE 125M

> >   AUTOEXTEND on

> >   NEXT 25M

> >   MAXSIZE 250M

> >  MAXDATAFILES 100

> >  MAXINSTANCES 2

> >  NOARCHIVELOG

> >  CHARACTER SET UTF8;

> >

> >Notice MAXINSTANCES?

> >

> >Daniel A. Morgan

>

> Sorry, Daniel, I don't get your point. If MAXINSTANCES is a parameter

> related to multiple instances for one database, it's called parallel

> server, as I can remember. My question is, however, about one database

> across multiple computers.

>

> Dino

>