MAXDB on LINUX use only one CPU

[Former Member]

Hi all,

I have a question regarding the usage of parameter MAXCPU. I have set it the value 3. But I do see only one cpu used and almost at 100% with the command "top".

My release is MAXDB 7.7 and the kernel for Linux is SMP.

Someone can tell me what influence this behaviour?

thank you all

[Former Member]

Hi,

The database kernel runs as one process divided into threads. Did you start top -H to check the Cpu-Usage?

Threads can be active in parallel on several processors within the operating system. Threads perform various tasks.

MaxCPU has influence on the number of Threads which are created during restart.

In your case after restart you have 3 Threads ( UKT ) -> you can check this with x_cons show all

How many threads are active in parallel depends on the distribution of the User Tasks on the Threads and the applications which are connected to the User Tasks.

x-cons <DBNAME> show active shows the status of the different Tasks in an UKT. Notrice that an UKT can contain several Tasks but at one time only one Task in The UKT can have the CPU.

MaxDb manages this via internal dispatching.

You will find more information about the process structure in the Expert Sessions recording and slides of session: Session 18: SAP MaxDB Architecture

You can download the session here ->   SAP MaxDB: The SAP Database - Training

Regards, Christiane

[Former Member]

Hello Christine,

thank you for the kind explanation. So apart during restart there's no other way to make maxdb use more processors?

So If I see one Always at 100% it's not a problem because it correctly and internally dispatch the threads.

Am I right?

[Former Member]

Hi Bruno,

you should have a closer look to the database.

Here you use the database console program x_cons

x_cons can be started in an interval so you can see the status of the database tasks and if there are really more CPU used.

x_cons <DBNAME> show all > all.prt    

-> tells the current situation/configuration ( only one snapshot)

x_cons <DBNAME> show act 5 10   > act.prt 

-> creates every 5 seconds a snapshot of the active tasks 10 times

You start both comamnds from OS level as User which has the database software environment.

those both files should help us to check what is happening on your database.

You'll find a documentation of the database consdole using the following link:
http://wiki.scn.sap.com/wiki/pages/viewpage.action?pageId=81428811

Regards, Christiane