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Low CPU usage and high wait rates

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Jose Mosquera
Honored Contributor

Low CPU usage and high wait rates

Since that we have migrated our Uniface 7.2.06 application to a new L3000-5x server with HP-11.0 64b and Oracle 8.1.7 64b (in the past in a K370 server with HP-UX 10.20 and Oracle 7.3.4) I have noticed the continuous presence of the "swapper" in the first page of the ???top??? command. Reading a ???HP-UX Memory Management White Paper??? has been able to understand that ???sched()", colloquially well-known as " swapper ", it is the responsible to handles activation and reactivation of processes when free memory falls bellow minfree, or when the system appears to be ???trashing???.

We have been able to feel high wait rates to some processes with a high demand of ???I/O??? while processors (3 x 550Mhz CPU???s) show us high ???idle??? percentages. This makes me think that we should have some ???Kernel??? parameters are not appropriate with the new hardware/software characteristics and that they can be causing "trashing" in the system due to some high "paging" levels and lower CPU usage.

Please find attached a zip file with additional information about.
5 REPLIES
Pete Randall
Outstanding Contributor

Re: Low CPU usage and high wait rates

How much memory does this machine have?

Pete

Pete
Justo Exposito
Esteemed Contributor
Solution

Re: Low CPU usage and high wait rates

Hi Jose Maria,

As I can see you have to high this parameter in your kernel.
dbc_max_pct 50 50 Static N/A

There are a lot of issues in this forum and the recomendations are from 5% to 10% depends on the total amount of memory in your system.

The minimun value must be 300MB, then you can try to put a low percentage, I sugest you that first try with 25% and look at the backup performance in order to know if this is a good percentage.

You can obtain more information about this parameter in the search section in this forum by trying dbc_max_pct.

Hope this helps,

Justo.
Help is a Beatiful word
Stefan Farrelly
Honored Contributor

Re: Low CPU usage and high wait rates


The reason swapper is so high is your system is very busy paging processes/memory out to disk and back. This is not a good situation to be in, it will slow down everything. You must reduce the memory pressure. As someone has pointed out your HP-UX buffer cache is too high(dbc_max_pct). Reduce it so that as a % of your total memory it wont use > than 300MB (not minimum as someone else said). Setting it to 300/350MB is fine.

After you do this and reboot your dont want to see the USED line for the device lines from swapinfo -mt > 0. This means no memory pressure and no paging. This will increase performance considerably.
Im from Palmerston North, New Zealand, but somehow ended up in London...
Jose Mosquera
Honored Contributor

Re: Low CPU usage and high wait rates

Hi Pete,

This machine have 4Gb RAM
Pete Randall
Outstanding Contributor

Re: Low CPU usage and high wait rates

Jose,

4Gb is on the low end for 11.0 64 bit. As previously pointed out, you need to reduce your memory pressure - probably by reducing your buffer cache (dbc_max_pct).

Pete

Pete