7.1 - Unable to free unused shared memory

If anyone has struck and/or resolved the following problem then any advice that could be offered would be appreciated. Environment: Sparc1000 running 7.1 DSA. 512 Meg Ram. Not a dedicated Informix Server. Problem1: When physical ram (as opposed to swap) gets down to near zero the logs (100 Meg on a 600 meg database with low transactions) start to fill at a rate 20 times normal usage. When memory is freed the log usage goes back to normal. Problem2: Attempting to free up unutilised shared memory segments does not result in the desired effect. Although the system claims to be using (say) 23 Meg (onstat -g ses). It still reserves (say) 125 Meg in shared memory. Running ipcs tells me that the segments are being accessed every minute even when there is zero user processes running. (oninits stay attached). onmode -F does not free segments. onstat -g seg says that many segmentshave a 2 (two) block utilisation, out of 2000 odd blocks. IE it appears that something is holding a lock on shared memory even when zero users logged in. The only way to recover shared memory is to roll online. most days if I get in real early I can manage this. I have logged this as a call with Informix but if anyone already knows the answer to this problem then I could sure use the extra sleep. Thanks Peter Tashkoff Auckland, NZ.