topic async driver in Operating System - HP-UX

async driver

Russ Docksteader — Mon, 05 Nov 2007 15:08:41 GMT

We have oracle databases using raw file systems and hence the async driver. The max_async_ports parameter is set to the default of 50. If I look at the number of processes using the async driver I see more than 50. It was my understanding that if the maximum number of async ports was reached, that any new process requiring disk I/O would use the synchronous driver. How can I see 88 processes using async when the max is set to 50?

Re: async driver

Steven E. Protter — Mon, 05 Nov 2007 15:14:50 GMT

Shalom

ports != procs

Ports not equal to processes.

Do you have a performance problem to deal with? If not, consider not passing go and making changes. If yes, what steps have you taken thus far.

http://docs.hp.com/en/5991-6469/ch05s02.html
Tunable on the fly in 11.31

SEP

Re: async driver

Geoff Wild — Mon, 05 Nov 2007 15:31:55 GMT

Is this the same Russ that worked with me at BC Gov in the early 90's?

Rgds...Geoff

Re: async driver

Geoff Wild — Mon, 05 Nov 2007 15:39:16 GMT

BTW - just because you see 88 processess using async - that is okay.

The key here is that if set to 50, a maximun of 50 simultaneous connections can be made.

Now, if you see waitng on I/O, then yes, you should tune this up.

Try in increments - say go to 75 and see if this improves performance...

Rgds...Geoff

Re: async driver

Russ Docksteader — Mon, 05 Nov 2007 16:27:22 GMT

Steve,
We have a mix of machines, some with poor I/O performance, others are okay. The dba is recommending setting max_async_ports to 520.
Any issues with setting it this high?

Geoff,
Darn tootin'! I thought that was you. How are you doing?

Any guidelines for setting max_async_ports other than setting it to less than nproc?

Regards

Re: async driver

Geoff Wild — Mon, 05 Nov 2007 16:32:45 GMT

Russ - you can contact me here:

http://www.met.ca/itrc/index.php?option=com_contact&Itemid=3

520???? Whoa...from man page:

The resources for the port are allocated from the kernel memory.
Setting a higher value would result in the driver using more kernel
memory. Other kernel components which may need kernel memory could
suffer.

So, I don't know how much kernel memory is used per async port - but I assume jumping 10 times could impact your overall system performance...

Rgds...Geoff

BTW - I'm doing great!

Re: async driver

whiteknight — Tue, 06 Nov 2007 03:21:03 GMT

Russ,

There is an i/o performance if you tune max_async_ports too high which caused all the space to be allocated as buffers.

It is recommended you follow Oracle advise and the value they suggest not too high.

ok to proceed

WK

Re: async driver

Russ Docksteader — Tue, 06 Nov 2007 10:14:54 GMT

Since the man page for this tunable indicates that there is no recommended value, I am going to go with the dba suggested value of 520 (the value of nproc) and see what happens. I've got a cople of new machines running HP-UX 11i v3 so at least I'll be able to test the values here dynamically without having to do a reboot.
Thanks for your responses.

Re: async driver

Russ Docksteader — Tue, 06 Nov 2007 10:30:37 GMT

Seems as though there is no hard and fast rule here, so I will use my HP-UX 11i v3 machines to test the values dynamically. Thanks for pointing that out Geoff.