Adding Memory to HP 10.20

[melvin mariney]

Hi,

We are in the process of adding 1GB of memory to a 10.20 D class server which currently has 2.5GBs of memory.

As far as kernel parameters or patches, is there anything that needs to be looked at to make sure that this memory is utilized?

We have Informix applications on the server that use a lot of shared memory. Are there any changes needed for shmmem kernel parameters? Should 'magic' numbers be changed for applications?

Also, for 3.5gb of memory, how much swap space should be allocated and should psuedo-swap be used?

Thanks in advance,

Melvin Mariney

[John Palmer · Accepted solution]

The system will automatically use the new memory. You don't have to change any kernel parameters specifically for the system and you don't need any new patches either.

You may need to amend some kernel parameters (such as shmmax and maxdsiz) in order to let your applications use more memory. Remember though that shared memory is limited to 1Gb per segment and a system maximum of 2.75Gb by the 32bit architecture.

I would always have swapmemon=1 as it reduces the amount of real swap space that you need by a 75% of your real memory. Adding 1Gb of real memory and having swapmem_on=1 will actually reduce your real swap requirement by about 750Mb! Check out swapinfo -t after adding the memory.

As to actual swap space, you will need what you need. If you have an idea of how much additional process data space you will be allocating then that is how much additional swap space that will be required. You really need to monitor swap usage while loading your applications to get a real idea of what you need.

Hope this helps,

Regards,

John

[CHRIS_ANORUO]

Hi

Set DBC_MAX_PCT=25 so that buffer cache will grow to 25% of your Physical memory. I encourage you to use swap space of 1.5gbyte since you have enabled pseudo swapping.

Regards

[Alan Riggs]

I recommend that you do not increase dbc_max_pct to 25%. Actually, properly tuning buffer cache requires some investigation of whether your disk access tends toward read intensive or write intensive, whether other applications (like oracle) do internal buffering of writes, etc. As a general guidline, though, performance of the sync command starts to override benefits of write caching when the data structures grow above 300 MB (at 10.20, at least). For a system with 3.5GB of RAM this would mean a dbc_max_pct of about 8-9% would be a good "generic" starting point.