informix kernal parameters

[someone_4]

Hello,
I am looking for the kernal parameters for an L2000 server that is going to be running informix.

I got the following from the
MACHINE SPECIFIC NOTES FOR
IBM Informix Dynamic Server 9.30.FC3 PRODUCT RELEASE ON HEWLETT PACKARD HP-UX.

nfile: 5000
semmni: 3000
semmns: 3000
semmnu: 1400
shmmax: 4294967296
shmmni: 500
shmseg: 500

But I was wondering if anyone had any recommendations on other parameters for good informix performance.

Thanks,
Richard

[Zafar A. Mohammed_1]

It also depends upon how big your instance(database). There are other parameters also which you need to check i.e. informix onconfig file. Allocate proper buffers, locks, shared memory parameters.

Thanks
Zafar

[Michael Tully]

Hi Richard,

Depending on how many instances you plan to run, these parameters should serve you okay. We run four instances with this on a L3000. The amount of shared memory is always a issue. This will depend on whether your attempting to run the instance(s) through tcp or shared memory. See attached file. Unfortunately I can't help with the Informix internal parameters.

Regards
Michael

[JJ_4]

Hi,

Well, the one parameter that interested me on "Michael Tully"s attachement was the dbc_max_pct being set to 50. I was led to believe that this will actually reserve 50% of real RAM for file system cachung. Obvsiouly, with 4 Gig of RAM on a machine, to dedicate 2 Gig to file system caching is ... bad - 128Mb should be fine. I have seen issues where people could not get informix resident because of this parameter.
As far as kernel parameters for informix go, well keep an eye on the number of available file descriptors depending on whether you are using KAIO or AIO. If you are using AIO and have a lot of AIO VPs and chunks, then multiply them together and add bit of overhead and that will be the minimum requirement for nfiles. Use sar -v 5 5 to get an idea of how many open files your system has etc. etc.

[Michael Tully]

Interesting pickup there on my dbc_max_pct value. I'll have to check that particular system when I'm in the office next. Mind you this was a development server, so I'm not too concerned. The buffer cache value has has been posted many times should be around 300Mb of RAM.

[Steve Lewis]

Richard,
My L2000 with 2Gb of RAM and 2 instances has these extra values:
dbc_max_pct 15
semume 512
nkthread 2048
max_thread_proc 256

You can comfortably reduce shmseg to 128.

Also add drivers: asyncdsk and asyncdsk_included to enable kernel asynchronous i/o. You then create the device file: mknod /dev/async c 101 0x0
Then export KAIOON=1 and IFMX_HPKAIO_NUM_REQ=3000 for user informix before you start the instance.
Steve

[Pete Randall]

dbc_max of 50 is not the killer. Max means the most memory that will be reserved if needed, not that it's going to take 50% off the top. With dbc_min set to 5, you should be OK. I've run Informix with these settings for years with no ill effects.


Pete