need advice: two db instances on one box?

[Hofmaenner]

We are setting up a new server running SAP R/3. Now my boss wants another database (not directly related) installed without spending much more money. I am pondering wether we should use new hardware, implement virtual partitions or use prm. Is there something called soft partitions on hp-ux or is that a synonym for prm?

[Stefan Farrelly]

We run up to several db instances on the same box without any problems. As long as they are the same product (SAP or Oracle - dont mix them on the same server) and you have enough memory (tons) and cpu power then a single box can cope fine.

I dont think you need to bother with virtual partitions (running multiple instances of HP-UX on the same server). PRM is process resource manager - for controlling the amount of CPU indivdual processes or groups of processes use. I dont think this is necessary either - unless you are going to be tight on cpu power and one db uses an unfair amomunt of cpu compared to others.

[Hofmaenner]

What bothers me is that we are implementing a high-availability solution (99.99...% :-) on a hp superdome and i don't like to get downtime caused by another db (installing patches and the like).

[Nick Wickens]

We run several database instances (informix) on a single K class machine without any problems but we do have to add extra memory to cope with each extra instance.

We also give each instance its own userid base and group (ie the users have to login with a different ID for other instances) which can be usefull at a later date if you did want to start using PRM as you can then put all of the second instance users and processes in a lower PRM group.

[Ravi_8]

Hi,

you can create 2 database instances in one box, make sure u have sufficient space and swap.

[Tim D Fulford]

With the above resource limitations.

I do not know whether you are running Informix or Oracle (or something else), unfortunately they both use the word instance but it means slightly different things.

In IBM-Informix it is possible (easy) to create a new databse whithin the same instance. I would only reccommend that the new database has it's own dbspaces/chunks so that in the future you could easily seperate it out & migrate it with little effect in the original databases. I also believe Oracle is similar in this respect.

This will mean there will be a reduction in the number of processes (pid's) running to service the databases. Also you will only have one set of redologs/physical & logical logs etc, this will save on disk space. Lastly you will only require one set of buffers in memory so a saving on memory.

The only caveat I would make with the avbove suggestion is that if one database is OLTP and the other is OLAP of bulk load/unload it would be better if they were seperate & preferably on seperate boxes (as there is likely to be disk contension )

Tim

[Hofmaenner]

We are using Oracle (Version 8_17). My problem is that i definitely want as less dependencies as possible between the dbs because of maintenance. We (except our boss for bugdet reasons) like to have a dedicated server and i am looking for a compromise with least disadvantages.

[Tim D Fulford]

Hi

If you want to utilise the minimum of resources then create a new DB utilising the same instance. If you want to really make things migratable dedicate a lister thread to it. I THINK you can do this in Oracle (certainly can in Informix), even create a alias to the instance name.

You will preserve the most resources by doing this. If you are short on any of the following disk, memory, CPU then creating a new instance will stress it more. If not then a new instance will certainly keep things seperate.

Tim

[Tom Geudens · Accepted solution]

Hi,
Argumentation for dedicated servers :
- Applications/Databases have different Service Level Agreements (different downtimes)
- One of the databases is a datawarehouse/olap database
- The applications that use the databases are (different) third party softwares (this kind of software often needs exotic patches and/or will often call for the latest databases patches).

Argumentation for multiple instances on same server :
- Unless we are talking about big databases the utilisation ratio of the server will be better. In fact, if the databases are really small, you should consider consolidating them in one instance.
- Upgrades will take less time (since you've got the software on only one server).

Other points :
- When dedicating a server as "database server" you should make SURE the applications are on another server. You cannot (most of the time) tune for both databaseperformance and applicationperformance.
- The idea of using two seperate listeners is a good one. We use it to easily distinguish the oracleprocesses of two instances (which makes using MeasureWare and PRM easier).

Hope this helps,
Tom

[Dan Herington]

We have two different types of "soft" partitions (virtual partitions and resource partitions) Resource partitions is PRM.

We have thousands of customers with multiple oracle databases running with PRM. This is a very robust solution. We also have many customers running multiple instances of SAP with PRM.

Advantages of PRM over vPars is lower admin overhead because you are running multi partitions in one OS instance. You also get maximum flexibility as every CPU tick can be allocated used some workload if the workload that "owns" it doesn't need it. This increases utilization. Also, vPars requires duplication of all I/O hardware. In a high availability environment this can mean a lot of extra hardware.

Advantages of vPars - separate OS instances. This is useful if you have apps that have port or namespace conflicts. (which you won't have if you are running 2 Oracle instances) vPars is better than multiple systems because you can dynamically move CPUs from one vpar to another to improve the utilization of the CPU. Although, this isn't automatic unless you use Workload Manager.

Workload manager is a product that will monitor the performance of your databases and reallocate the resources to ensure the highest priority databases get the resources they need to meet configured service level objectives.

There are whitepapers on how to use PRM and WLM with Oracle on our websites:

PRM: http://www.hp.com/go/prm
WLM: http://www.hp.com/go/wlm

These websites are managed by us here in the lab, so the info is both up to date and fairly technical.

Dan