In article <buujgtkhgvqg6rlj0586fddq5bsntv6jq4_at_4ax.com>, "Dino Hsu"
<dino1_nospam_at_ms1.hinet.net> wrote:
> 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
>
You're almost there, Dino.
MAXINSTANCES is a 'CREATE DATABASE' parameter. In this
case, it indicates that this database will be able to support, at most,
2 instances. So, you have one database (one set of control files,
data files, log files), and two instances (sets of executing processes
and related memory, semaphores, shared memory segments, etc.)
If both instances are on one computer, it's not very interesting, so....
What if we take the database (set of control|data|log files) and
put it on some type of clustered file system(s)....?
Now, mount your cfs filesystem(s) on two separate computers, and
guess what you can do? That's right, one instance per computer.
And, there you are: one database, two computers.
In a nutshell, it's OPS.
-Mark
Received on Tue May 22 2001 - 01:05:34 CDT
