Re: Database that spans over multiple computers

On Tue, 22 May 2001 16:39:59 +1000, "Howard J. Rogers" <howardjr_at_www.com> wrote:

>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
As I just read mag articles about the latest development of storage devices, you probably are talking about NAS (Network attach storage) or SAN (storage area network), which share a group of disks to multiple, possibly heterogeneous, servers. Each server will treat these disks as if they are local disks; one database residing on this storage device can be activated on muliple servers with the Oracle Parallel Server funcionality. The purpose of this is to share the workload to multiple computers. However, if multiple instances of one database are activated on only one server, I don't see any usage.

Dino Received on Tue May 22 2001 - 07:15:48 CDT