Re: 20 Instances 1 Machine

Your biggest problem is not going to be physical RAM or disk space (either of those could simply be purchased large enough). However, you *will* encounter a problem with "Shared Memory".

32-bit (and even 64-bit) operating systems have a finite amount of "shared memory" addressable for use by 32-bit applications (namely the RDBMS shipped with the Oracle Applications). This number is 1.7GBytes on HP/UX and, I think, 2GBytes on Solaris. This "Shared Memory" limitation is systemwide. The Oracle RDBMS uses shared memory heavily for major components of the SGA. As a result, if you're running a 32-bit version of Oracle, this number represents the sum of all SGA's running on that machine at the time. (So, at 500M/instance, you'll run out somewhere between 3 and 4 instances).

Possible solutions would be:
1) Use a 64-bit version of the Oracle RDBMS as certified for your platform.

    A 64-bit version of Oracle would address shared memory from a much larger     total pool (most likely an absurdly large number), thus avoiding this 32-bit     "Shared Memory" problem.
2) Consider using something like Sun's "System Domains" to partition a big box

    into multiple "virtual machines". Each of these Domains would have it's own     shared memory pool.
3) Consider using seperate machines.

Personally, I'd vote for seperate machines. I tend to prefer only one production system exist on any given host as it tends to eliminate much of the performance-oriented fingerpointing that is bound to come up. Additionally, running a large number of production instances on a single host can be alot like putting all of your eggs into one basket. It may be cheaper, but if something happens to that basket, everything's hosed.

As far as hardware:

        Lots of disk, plenty of I/O channels, and plenty of CPUs. Without actually knowing the nature of your applications, I'd say you're probably looking in the SunFire 6800 or SunFire 15k range (if you're looking at Sun equipment).

Post, Ethan wrote:
> I got a request to spec out a machine that could handle 20 separate Oracle
> instances on a single UNIX server. SGA should total about 500 MB per
> instance. We have some hosts here with 6-8 instances but never tried 20
> before. Wondering what types of things I should be worried about, obviously
> having enough memory but are there any other limitations I can expect?
> Anyone had to do this?
>
> Thanks,
> Ethan

• James

  ---

  James J. Morrow E-Mail: jmorrow_at_warthog.com Senior Principal Consultant Tenure Systems, Inc. McKinney, TX, USA

"The reasonable man adapts himself to the world: the unreasonable man

   persists in trying to adapt the world to himself. Therefore all progress     depends on the unreasonable man." -- George Bernard Shaw

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