RE: real-time scheduler in Solaris?

From: Guy Hammond <guy.hammond_at_avt.co.uk>
Date: Wed, 13 Jun 2001 10:52:56 -0700
Message-ID: <F001.00328046.20010613094702@fatcity.com>

The real time scheduler is really for applications that need to respond in "hard" time, for example control of industrial machinery. Hard scheduling wouldn't necessarily result in higher throughput, it would only result in predictable response times. You may be able to get very fast responses, but you are trading this off against lowered concurrency, as the only way to guarantee a response within a given time is to ensure that you have the resources available to do so.

Similarly, changing the priority of processes doesn't buy you very much, as you will be creating a bottleneck at the lowest-priority process. And "nice" is only a hint to the scheduler; it is by no means mandatory. Solaris doesn't really support what you want to do, which is to define minimal levels of system resource availability on a per-process basis (you can do this on OS/390 and VMS).

If you are running on high end Sun kit, you can logically partition the system, for example you could reserve a group of CPUs for an instance of Solaris that ran Oracle exclusively, segregating it from the other applications running on the machine. In effect, you are making one physical server behave as multiple logical servers, each one running its own Solaris and behaving essentially as a separate machine. The benefit of this approach over and above just moving Oracle to a separate machine is that you can shuffle CPUs around between partitions, for example during periods of peak load, add more CPUs to Oracle, but perhaps overnight move those CPUs to another task (perhaps running batch jobs in a separate instance, or even non-Oracle, compute intensive jobs). Doing this would mean that you had to retune PQO (and possibly other variables also if it corresponds to large load spikes, and you can take the time for a restart) every time you added or remove resources from the partition. For example, if you added more memory to your partition you might want to alter the SGA.

It will be a mild performance hit, but if you want to know what is really using system resources in your system, try running with process accounting enabled for a while.

Cheers,

-----Original Message-----
Sent: 13 June 2001 16:21
To: Multiple recipients of list ORACLE-L

Two comments:

Why not just re-NICE the shadow (or offending procs)
Last I heard oracle does not recommend running their procs at differing NICE levels.

-----Original Message-----
Sent: Tuesday, June 12, 2001 6:33 PM
To: Multiple recipients of list ORACLE-L

Folks,

Does anyone know how to exploit the real-time scheduler in Solaris? I can only find vague references to this on the web.

We're considering using the real-time scheduler for Oracle background processes on our busiest Solaris boxes (that support 2-3k connections). We want to make Unix bias the Oracle background processes for CPU, all other things being equal. We had some consultants suggesting our MTS config wasn't getting the cycles it needed after we called into question their SQL (which is too long a story for me to get into -- I'll begin ranting about big consulting companies. :)

Thanks,
Steve

Steve Austin
DBA for Unix-based systems
Enterprise Data Center Operations, XO Communications email: ssaustin_at_xo.com

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