INFORMIX W/HP-UX gurus

[Byron Myers]

N4000, HP-UX 11.0. INFORMIX V7.31.FC7XE1.
nfile HP-UX kernel parm set to 35000. INFORMIX NUMAIOVPS parm set to 140. These settings resulted in a max file table utilization of 21000 (about 60% of file table). We bumped NUMAIOVPS to 232, and the UNIX file table went to 100% - after adjusting nfile to 70000 we see that the max utiliztion of the UNIX file table is at about 38000.
Question: how does bumping INFORMIX NUMAIOVPS from 140 to 232 increase the number of files open from 21000 to 38000 (17000 difference)?

[Candido Caceres]

Hi Byron,

Did you receive any answer to this question?? I have a similar problem with an extensive use of nfiles. In one of my systems with Informix and HP-UX 11i, I have the NUMAIOVPS param set to 250... but I have 180000 in nfile and it is just enought to support three weeks more and less!!!

[James Murtagh]

Hi,

I don't know Informix too well but I'll have a stab at it. If I make incorrect assumptions let me know.

I assume NUMAIOVPS (Number of Asynchronous IO Virtual Processors?) are kernel threads used by Informix when KAIO is enabled. I believe Informix suggest setting it to the number of cooked files + 1 in this case.

Assuming you have more threads to access the files the file table entries will rise proportionally - remember this table is really the number of file opens - you open the same file twice and you will have two entries in the table. Looking at your figures:

140 VPS --> 21000 opens
~ 150 opens per VPS
Add an extra 92 VPS ~14000 extra opens = 35000 opens

So this is not too far off what you witnessed. Does this sound reasonable?

Regards,

James.

[Byron Myers]

I think James is on the right track - I have yet to find a definitive answer. I believe my system is behaving as follows: 155 chunks are defined in INFORMIX (close to what James is saying with 150). So 155 chunks times 232 NUMAIOVPS is roughly 36000 - somewhat close to 38000. We have recently set NUMAIOVPS to 302, now the file table utilization is about 40000. So 155 chunks times 302 = 46810, somewhat close to 40000. I believe there are one or more other factors in calculating the possible number of open files here, but I used the formula above (NUMAIOVPS * number of chunks) to derive a minimum value for the HP-UX kernel parm "nfile". I take this minimum and double it for safety. I have 4 other INFORMIX instances that are behaving as described above. Since setting nfile accordingly on each of these INFORMIX instances (5 total), I have not had any problems with a UNIX file table filling up.

[Zafar A. Mohammed_1]

Hi Myers,

In Informix, to findout the NUMAIOVPS:

If the database server implements kernel-asynchronous I/O, but you are using some cooked file space, allocate two AIO virtual processors per active dbspace that is composed of cooked file space. If kernel-asynchronous I/O is not implemented on your platform, allocate two AIO virtual processors for
each disk that the database server accesses frequently.

NUMAIOVPS formula:
= max((2 * number_of_chunks), 6)

where number_of_chunks is the number of chunks that you have allocated

Thanks
Zafar

[Byron Myers]

It took me a while to find the one posted question for which I didn't assign points to a reply - fixed now!